Controversies in Heterogeneous Classrooms, Adolescents’ Experiences of Social Cohesion in Brussels and Its Schools

: As globalisation changes the sociocultural architecture of urban areas, adolescents increasingly interact with different sets of values and worldviews, which can be a potential cause of conﬂict and anxiety. To date, there is little empirical research on how adolescents perceive and experience social cohesion in a superdiverse metropolitan context such as the Brussels Capital Region. In this study, we elaborate on the relationship between social cohesion and ethnic diversity, using controversial topics as instruments to examine the erosion of social cohesion. To expose these processes, 34 in-depth interviews were conducted with pupils from Dutch-speaking secondary schools in Brussels. Through thematic analysis, the data revealed four overarching themes of controversies: Brussels, religion/philosophy, ethnicity/national belonging and political horizon, epitomising a paradox of conﬂict and consensus. Notably, during the interviews, the adolescents reported a climate shaped by actions of ‘silencing’, ‘avoiding’ and ‘voicing’ when discussing controversies in a heterogeneous classroom context. This analysis of adolescents’ perceptions of social cohesion hence corrob-orates the premise that conﬂict is not the opposite of cohesiveness, but rather an integral part of a pluralistic society.


Introduction
In the aftermath of the terrorist attacks in France and Belgium, the emphasis to discuss topics such as "freedom of speech", "terrorism" and "radicalisation" in the classroom has led to tensions, especially among teachers and students. Indeed, classes in European metropolises such as Brussels and Paris are superdiverse, while these concepts originated within the specific contexts of 20th-century nation-states. Despite the likelihood that these topics are polarising in a classroom setting, we have insufficient insight into the impact of the curricular interventions, as empirical evaluations of them are scarce [1][2][3].
We aim to understand the processes of social cohesion and polarisation amongst young people and scrutinise how these processes unfold. To this end, we focus on the Brussels Capital Region, because of its young demographic structure and high degree of ethnocultural diversity [4,5]. Arguably, urban areas across Belgium and Europe will increasingly resemble a city such as Brussels as processes of globalisation continue [6]. In this context, with a diversity of languages, ethnicities, religions and cultural practices, the presence of a consensus of minimal overlapping values (cf. [7,8]) seems to be contested in everyday practice. Interaction in public spaces is supposed to be governed by shared expectations and rules in social interactions. One of these 'first lines' of interactions in which we find contestations of this minimal overlapping consensus is the school. The current contribution wants to shed light on the impact of controversial topics in the classroom context.
Against that background, we operationalise the nexus between the erosion of social cohesion and the discussion of controversial issues. There is a fair amount of quantitative evidence on the incidence or the degree of social cohesion in ethnically diverse societies (for an overview, see [9,10]). Still, these results are mostly debated among scholars, which offers young adolescents little room to express their views on social cohesion (cf. [11][12][13]).
Nonetheless, in social cohesion research, we deem it fundamental to examine how young people-especially during their formative years-feel they are part of society ( [14,15]). Moreover, adolescence is a formative period in life that has an important and lasting influence on young people's view on society [14]. Additionally, cognitive development and social learning during this period are notable in adolescents' lifelong identification, civic engagement and openness to change (Sears and Brown, 2013). In this respect, schools offer an intrinsic role. Adolescents are de facto socialised in the school context and are, consequently, a significant component of the configuration of social cohesion [16,17].
Brusselian youngsters grow up "in a vast ethnic, cultural and linguistically diverse context, which has been considered super-diverse, [ . . . ]" [18,19] and in a highly dualised metropolitan context that shapes plural identities [20]. Accordingly, Brussels is considered a salient social laboratory [6] to investigate potential symptoms of social cohesion's erosion. More generally, the interviews inquired how the adolescents perceive and experience themselves-as members of the Brussels society-and how controversial topics undermine their notions of social cohesion. More specifically, this article answers the following research questions: How do sensitive subjects manifest in a pluralistic classroom context and with what repercussions? What are the major common factors regarding the consolidation of social cohesion?
The structure of this article is as follows. First, a brief overview of the current literature regarding social cohesion and its relation to ethnic diversity is presented. In addition, we provide a short literature overview regarding controversial topics in the classroom. Second, we present the results of the data based on a thematic analysis in NVivo 12 [21]. Finally, the conclusion summarises the major findings, providing an outlook on possible future research and outlining a few key limitations.

Controversial Topics in a Super-Diverse Classroom Context
As globalisation changes the architecture of urban areas, we glean from the scientific literature that various issues incite strong feelings and divide opinions in heterogeneous classroom contexts. Concretely, curricular topics-ranging from the scientific theory of evolution to colonialism, LGBTQ-rights and the Holocaust-that were deemed closed questions are increasingly experienced as controversial among school officials, teachers, students, parents and peers [22][23][24][25].
Although prior studies have theorised how controversial topics weave throughout time and across contexts from open (currently debated) to closed (resolved) controversies and vice versa [26,27], few studies offer an overview of how these conflicts are fuelled by identities embedded in diverse social, political and ethno-cultural contexts [22,23,28].
We deem that controversial topics epitomise the straining of social cohesion as classrooms become more heterogeneous. From the available literature, we learned that some curricular topics are perceived to be controversial because of the normative value judgements attached to them [29], resulting in conflicting narratives of belonging, identification, shared values and norms [27,30,31]. The discrepancies can become divisive or 'too hot to handle' [32] (p. 306), guided as they are by a lack of nuanced or shared information, conflicting worldviews and different value systems, rather than an active search for common ground [29,33]. As such, controversial issues exhibit similarities with the erosion of social cohesion, as documented by Schiefer and van der Noll [9] above.
In turn, controversies are an inevitable part of a pluralistic society. Education is therefore widely regarded to be an important vehicle to cultivate social cohesion [34]. After all, the acquisition of civic values, knowledge and skills is expected to take place-at least partially-in schools, through formal education and socialisation [14]. Accordingly, Zimmerman and Robertson [33] endorse that adolescents, as future citizens, should be exposed to engaging discussions about issues that divide us. Empirical evidence corroborates their argument. Several sources assess that the relative diversity of students make classrooms compelling learning sites for acquiring the necessary skills to mediate the different narratives adolescents encounter on television, the internet and among their peers (e.g., [24,35,36]). In addition, prior research illustrates that engaging students in discussions helps cultivate their political engagement, critical thinking and tolerance (for an overview, see [37]). Therefore, it is necessary that schools and classrooms act as "a microcosm" of society, where students can practice democratic guidelines [38] (p. 258).
Introducing controversial issues in a structured manner may thus exemplify cohesiveness and conflict. Following the reasoning of Bickmore [39], controversies are similar to oxygen, an inevitable yet vital element of coexistence. In sum, whether a conflict occurs in a destructive or constructive manner depends on how it is handled [39]. Building on the preceding arguments and the definition of Hickman and colleagues [40], which is discussed below, we expect that controversial topics might articulate the coexistence of conflict and consensus. Moreover, conflict is thus not necessarily a negative outcome.

The Ethnic Diversity and Social Cohesion Nexus
To assess the attitudes of Brussels' adolescents, the present study utilises social cohesion as a theoretical framework. Although scholars have extensively discussed the concept of social cohesion due to its lacking conceptual conformity, Schiefer and van der Noll's [9] review concedes that definitions of social cohesion have more commonalities than is generally assumed. According to them, the literature attributes various idioms to social cohesion, including social relations (social networks, participation, trust, mutual tolerance), attachment or belonging and orientation toward the common good (responsibility for the common good, solidarity) [9]. Then again, some scholars warn against the normative connotation of social cohesion, assuming a perpetual deficiency of cohesiveness [41] and thereby vindicating the perception that globalisation-together with the growing diversity associated with it-erodes social cohesion [9].
Arguably, Putnam's seminal E Pluribus Unum [11], which reified the nexus between ethnic diversity and social cohesion, remains a salient starting point for previous discussion (cf. Savelkoul et al. [42]; Goodhart [43]). A different yet related concept to social cohesion is social capital, referring to the 'social networks and the associated norms of reciprocity and trustworthiness', [11] (p. 137). The scholarship regarding social cohesion seems to be intertwined with research on social capital. Social capital, however, refers to social networks and can take two forms, bonding with the in-group and bridging with the out-group. Both group processes are considered to be components of social cohesion [12,42,44].
Different forms of social diversity pose external challenges to social cohesion. Moreover, Putnam [11] states that, in the short term, ethnic heterogeneity reduces tolerance and solidarity among the in-and out-group within an ethnically diverse neighbourhood. In his research, he highlights how ethnic diversity undermines social cohesion, which he coined as the hunkering down hypothesis. However, a recent study shows that the correlation between ethnic diversity and social cohesion is complicated. Dinesen and colleagues' [45] meta-analysis study found that on average, there is a statistically significant negative relationship between ethnic diversity and social trust. Nevertheless, they state that "[ . . . ] apocalyptic claims regarding the severe threat of ethnic diversity for social trust in contemporary societies are exaggerated" [45] (p. 461). Since the results raise the question, "why is there a negative relationship between ethnic diversity and social trust?", they elucidate these outcomes by pointing to the lack of critical unknown factors. For example, the proper functioning of government institutions might be detrimental to the relationship between ethnic diversity and social trust. In sum, further empirical research is needed to elaborate on this negative relationship and to grasp crucial factors that are currently in a blind spot.
Conversely, compelling social psychological research by Gordon Allport [46] suggests that if specific conditions are respected, intergroup contact might lead to fewer prejudices, which Allport coined as the contact hypothesis. This hypothesis is the theoretical antithesis of Putnam's hunkering down [11]. A meta-analysis of Pettigrew, Tropp, Wagner and Christ [47] supported that intergroup contact decreases prejudices, especially among the majority group. Research consolidates the contact hypothesis of Allport and shows that intergroup contact has a positive impact on attitudes regarding diversity [47,48].
Following the dichotomy of Putnam's [11] hunkering down hypothesis and Allport's [46] intergroup contact hypothesis, social cohesion cannot solely be related to the degree of ethnic diversity, but equally depends on the conditions underpinning positive interethnic interactions. In the subsequent section, we therefore refine the conceptual and normative connotation of social cohesion by focusing on ethnic diversity and its constraints.
Precisely because of social cohesion's equivocal nature in the literature, we follow Hickman et al.'s [12] holistic definition. They describe social cohesion as "[ . . . ] the ability within the individuals and groups living in a place to manage the inequalities, differentiations and tensions intervening within and between them in terms that they perceive as positive and successful" [12] (p. 13). Their definition allows us to go beyond the predominantly quantitative studies (for an overview see, [9,10]) conducted with respect to the nexus between social cohesion and ethnic diversity. After all, they concur with the paradox that a social setting can be both cohesive and conflictual, and that conflict and inequality are not the opposite of social cohesion [49]. Nevertheless, the duality between the alleged decline of social cohesion, on the one hand, and growing ethnic diversity due to globalisation, on the other hand, still resonates with scholars and policymakers alike [9,49] To study previous processes, we endorse the idea that the discussion of controversial topics serves as a novel qualitative instrument to monitor perceptions of social cohesion in a heterogeneous classroom context. After all, the assumption is made that the emerging controversies are a symptom of declining social cohesion, which is associated with globalisation.

Materials and Methods
With 180 nationalities and more than 100 spoken languages [4,50], the BCR was, in 2015, the second most ethnically diverse city in the world [51]. Brussels' school population reflects this vast diversity [52]. Various socio-pedagogical challenges arise when such a population swiftly grows and simultaneously gets younger [20]. Notably, prior research reveals that domestic markers, including socio-economic status and home language, perpetuate disparities in educational attainment between pupils with an immigrant background and Belgo-Belgians [53]. Furthermore, most of these challenges tend to coincide with Brussels' high socio-spatial segregation between 'ghetto' schools and 'elite' schools, reinforcing Brussels' ethnic and social dualisation [54]. As such, since they do not share the same education, leisure, mobility or lifestyle patterns, these different peer groups seldom interact. Most of Brussels' adolescents (between the ages of 12 and 25) grow up in a superdiverse [18,19] and highly dualised metropolitan context that shapes their plural identities [20].

Study Design
Prior research clarifies that studying social cohesion and ethnic diversity outside an experimental setting remains difficult [55], extenuating the few qualitative studies that scrutinise the nexus between social cohesion and ethnic diversity (e.g., [40]). Accordingly, we opt to study these processes in a definite context, such a heterogeneous classroom. As highlighted earlier, we deem the classroom to be an ideal social setting, since adolescents socialise at school [14,17]. As globalisation patterns unfold, these pupils increasingly interact with different sets of values and worldviews, which potentially causes conflict and anxiety [56]. Therefore, we argue that qualitative research regarding the perceived social cohesion among adolescents is salient. Moreover, insights on how adolescents perceive their world in terms of relationships to their peers, classmates, teachers and the rest of the Brussels society are crucial elements. Hence, prior to theorising social cohesion, we operationalised the concept of social cohesion in an abductive manner [57] to assess whether ethnic diversity undermines social cohesion. This explorative qualitative study focusses on Brusselian adolescents in Flemish (or Dutch)-speaking schools in the Brussels Capital Region.

Participants
Our analysis relied on 34 face-to-face, in-depth, semistructured interviews conducted between January and April 2018. The respondents were in grades 10, 11 or 12 and aged between 15 and 19 at the time. We selected this age in particular because it is during this crucial phase of life that political and social attitudes are framed that subsequently undergo little to no change [14,58].
After the first six years of compulsory schooling, when pupils are in their second year of secondary school, they are tracked into academic, technical or vocational tracks [59]. The selection of the schools is based on their educational tracking, as well as their ratio of pupils with a low socioeconomic background, acknowledging Janssens et al.'s [54] observation of Brussels' segregated schools. This resulted in a collaboration with five schools: one school with academic tracks and a high percentage of pupils with a low socioeconomic background (8 respondents); two schools with all tracks and a low percentage of pupils with a low socioeconomic background (5 and 7 respondents); two schools with all tracks and a high percentage of pupils with a low socioeconomic background (9 and 5 respondents). Unfortunately, schools with solely academic tracks and a low percentage of pupils with a low socioeconomic background declined our request for collaboration.

Data Collection
We located the 34 interviewees through diverse channels. The first step was the same for all five schools: the principal of each school received a formal letter in which we explained the research objectives and invited them to collaborate. After having the permission of the principals, the schools located the interviewees through diverse channels, following our guidelines, in which we applied purposive sampling to achieve a maximum of variety [60] in age, gender, ethnic background, track (general, artistical, technical, vocational) and their municipality of residence. Potential respondents were approached by the school secretary, a student counsellor or a teacher, and if they were interested in participating, they received an informed consent letter for their parents explaining the content of the research, the involved researchers, confidentiality, data protection and contact details of the researcher (at the time of this study, 2017-2018, the university did not require ethical advice; however, the researchers followed the standard procedure by, for example, using an informed consent letter). The interviews took place in an available conversation room or a classroom of the school. They were conducted in Dutch; however, since French is the predominant language in the BCR and many students had difficulties fully expressing themselves in Dutch, they were given the opportunity to switch, briefly or permanently, to French at any time during the interviews. As a consequence, a substantive portion of the transcribed interviews are a mixture of both languages. Before starting the interviews, the researcher once again mentioned her contact details, guaranteed confidentiality and emphasised that they could interrupt or end the interview whenever they wanted.
The outline of the in-depth interviews can be divided into three major themes. First, participants were asked about their social background and how they perceive their identity and intergroup contacts. The researcher also asked about their experiences regarding a sense of belonging to the BCR. Subsequently, there were questions eliciting which specific topics in the classroom evoke strong emotions and thoughts in them and among their classmates, and about how they react and what they say. Other questions referred to how teachers and principals act during discussions regarding controversial topics. The duration of the interviews ranged between one hour and an hour and a half. The interviews were subsequently transcribed, which facilitated the identification of four patterns through a thematic analysis [21].

Data Analysis
The data analysis consisted of four steps. Supported by the literature review, the following concepts were used as sensitising concepts of social cohesion, notably, trust, tolerance, prejudices, intergroup contacts, sense of belonging and what the respondents consider to be conditions of coexistence. First, each interview was individually coded; subsequently, we coded the interviews through an iterative process. Likewise, we coded the respondents' perceptions and experiences regarding Brussels, their residential neighbourhood, Brussels' ethnic diversity and the terrorist attacks in European cities. To draw parallels between social cohesion and controversial topics, we clustered topics that respondents experienced as arousing particularly strong emotions, both in themselves and among their classmates. Subsequently, we coded respondents' experiences regarding how teachers handle controversies in the classroom. Our coding of the interviews was thematically guided by two key aspects. Throughout the analysis, the pivotal concepts 'conflict' and 'consensus' emerged from the data.

Results
In this section, we present the nexus between social cohesion and ethnic diversity in a superdiverse metropolitan context. Building on the theoretical framework of our literature review regarding Putnam's [11] hunkering down hypothesis and Allport's [46] intergroup contact hypothesis, our interviews corroborate Hickman and colleagues' [40] conclusion that conflict is not the opposite of cohesion. Moreover, there is an interplay between Putnam's and Allport's hypothesis, i.e., conflict and consensus, respectively [9]. The leading question that we asked the interviewees was which subjects do you experience as sensitive or controversial in the classroom, and how do you experience them?

Conflicts in the Classroom
After we inquired about their general perception of social cohesion in the city of Brussels, we asked our interviewees about controversial topics that arose in classroom discussions. Various intergroup and intragroup controversies regarding ethnicity or national loyalty came up. The mentioned controversies often turned out to be shared across the schools, while the disagreements were embedded in their specific ethno-cultural identities [27], inciting strong and divisive discussions. During the interviews, several adolescents disclosed that they experience peer pressure to conform to a specific value system: '[ . . . ] they say I'm a Flemish-Moroccan, and they say 'you don't act like a real Moroccan'[ . . . ]' (Respondent 17). Likewise, Respondent 11 felt threatened, 'they just attack you and say: 'you don't wear this, you don't wear a scarf, you're not like us, you should be Moroccan like we are, you should be proud'. At that point, I feel betrayed because the only thing they think about is violence . . . like violence is the only solution'.
Furthermore, as the interview took place in the aftermath of the 2015-2016 terrorist attacks in European cities, we queried adolescents' experiences and perceptions of these atrocities. Without any exception, all respondents disapproved of the terroristic attacks. Nevertheless, delving further into these unforgettable events, we specifically asked interviewees about their thoughts on Charlie Hebdo's cartoons, whereby we discovered that 19 of the 34 respondents disapproved of the use of humor with respect to religion. Some even stated that cartoonists such as Charlie Hebdo should be limited by law (e.g., Respondent 7, 18 and 33). Respondent 24 described how the Mohammed cartoons provoked controversy between her classmates, "There was a heavy discussion about it. The Moroccans said: 'no, you don't draw Mohammed', while the Belgians opposed: 'yes you can, that's freedom of speech'". Respondent 8 described the reaction of the teacher during a similar discussion, "I saw how the teacher [ . . . ] was shocked when the pupils approved of the terrorist attack on Charlie Hebdo". Seemingly, these respondents often experience this blasphemy as a lack of respect towards Islam and Muslims.
Twelve respondents with an immigrant background expressed compassion and a sense of injustice regarding geopolitics. Seven interviewees expressed their dismay toward Brussels' educational institutions, as their teachers and principals did not address specific events or topics. Respondent 6, for instance, recalled the commemoration of the Brussels' terrorist attacks, during which her school principal silenced the victims in Syria, Palestine, Turkey and other countries. When she asked the principal why he did this, he did not react. The same respondent highlighted that not being acknowledged filled her with strong feelings of resentment. Another respondent indicated that teachers are reticent when it comes to sensitive topics in their classroom, "[ . . . ] during religion class [ . . . ] we do not even discuss the differences between Islam and Christianity" (Respondent 32).
In terms of attachment to ethno-cultural group cultures and gender, five respondents experienced immediate disparagement from intragroup peers when they attempted to discontinue certain traditions or beliefs (Respondents 5, 7, 11 and 24). Respondent 25 reported a divisive discussion between male and female pupils of Moroccan origin on the persistence of gender-related role-patterns and whether women should stay home to raise children. "You saw that the girls expressed their outrage. One said: 'do you think that we go to school for nothing?'" (Respondent 25).
These excerpts illustrate that identity-related controversies are common in ethnically diverse groups. Two other respondents (24 and 25) recalled that the school organised a project highlighting LGBTQ rights following an incident in the classroom where Moroccan boys disapproved of homosexuality on the basis of their religious beliefs: "[ . . . ] many Moroccans [in my class] do not agree, they say 'God says it is not allowed, the Quran says this and that'" (Respondent 24). "Yes, there was a lot of discussion about that [ . . . ] Others, who were in favour of LGBTs said: 'that has nothing to do with who you are, your gender, who you like. It has nothing to do with religion. Religion has nothing to do with who you fall for, it's more personal'. Well. That was quite a discussion" (Respondent 25). Respondent 5, for instance, recalled a classmate stating that if his brother turned out to be gay, he would murder him. Although she and her classmates tried to convince him that using violence would be wrong, Respondent 5 felt powerless.
Despite the fact that Darwin's evolution theory is part of every Belgian educational curriculum, and its study material might cause controversy in the classroom, this subject was poorly mentioned by the interviewees. Respondent 1 recounted a discussion during French class when two pupils and a teacher were having a discussion regarding the evolution theory. When the Muslim pupil announced that she did not believe in the evolution theory, and the Catholic pupil endorsed that by saying that she shares the same opinion, the teacher said to the Catholic pupil: " 'I thought you were smarter.' These reactions [from the teacher] really irritate me" (Respondent 1). This demonstrates that when adolescents perceive teachers' reactions as disrespectful, it decreases their experience of an open classroom.

Consensus in the Classroom
First and foremost, we can say that a regional attachment to Brussels is prevalent among Brusselian adolescents. Of our interviewees, 26 expressed that 'being from Brussels' is a central component of their identity. For most of them, their sense of belonging is derived from cohesiveness in their neighbourhood (e.g., Respondent 1 and 20), an intraregional feeling of recognition (e.g., Respondent 11,14 and 18) and an affinity toward Brussels as a social entity (e.g., Respondent 19 and 26). Notably, this identification manifests a form of championing for their city. Various respondents adopted a protective attitude toward the prejudices of Brussels' superdiversity (Respondent 10) and some vigorously reacted against the stigmatisation of Brussels as a cradle of terrorism (Respondent 29). As Respondent 24 summarised, "I think we are a distinct region. Especially because we show Flanders that we are one group. Not in every regard-not regarding religion, etc. But we illustrate that we are together and stand up for Brussels [ . . . ]". At the same time, however, we noted that their friendships are subject to unwritten rules. As interviewees 8 and 9 disclosed, their cohesiveness is largely rooted in a climate of silencing to avoid discussion or conflict. "I avoid subjects about religion, because most of my friends are religious and we have different views about that", Respondent 8 explained. She continued by saying, "I don't like to discuss those [issues]-otherwise, we quarrel" (Respondent 8). Similarly, Respondent 9 stated that during discussions about religion or politics, "I would just listen, and I would not react". These examples show us that idioms of social capital are present in our respondents' daily interactions. Twenty-nine respondents implied both bonding with peers of the same ethnic background, as well as bridging with peers of a different ethnic background, thereby actively cultivating social cohesion among members of their in-group (same social, religious or ethnic background) as well as with out-group (of other backgrounds) contacts. Quantitative research within the project confirms these findings.
Due to Brussels' vast diversity, we also queried our interviewees about their plural identities. The majority explicitly identified themselves with various socio-demographic markers, including their origin, religion and language. For instance, Respondent 14 identified herself as: 'Brussels' Bulgarian'. In addition, the majority consider having friends of a different origin, skin colour and philosophy of life to be an added value and important to come into contact with.

Discussion
The aim of this paper was to improve the understanding of the relationship between social cohesion and ethnic diversity by using controversial topics as an instrument that illustrates the consensus-conflict dichotomy. Although a consensus of minimal overlapping values seems to be contested (cf. [7,8]), it has the potential to be reconstructed. Overall, this study rationalises that the dynamics of social cohesion, ethnic diversity and controversial topics coincide in the educational context. Adolescents experience that social cohesion erodes with the latter three, whereas Brussels' identity is conciliatory. With the exception of two respondents, all respondents experience Brussels as an empowering metaphysical unity where they feel home. 'Social networks and the associated norms of reciprocity and trustworthiness' [11] (p. 137) are as such deemed a principal component of social cohesion.
Schiefer and van der Noll [9] suggested that social capital is paramount to a cohesive society. They found that various scholars endorse the principle that especially 'minority groups need to be socially included' (p. 12). After all, intergroup contact might decrease prejudices toward outgroups [46]. Our findings illustrate how pupils seem to both bond and bridge [11]; moreover, most respondents find their ethnically mixed friendships to be a natural consequence of living in the BCR and are proud of it. The social relations necessary for cohesiveness are not inaugural, for it is the social entities in which social networks emerge that constitute social cohesion [49,61]. Whereas prior research has continually claimed that social identities might result in intergroup behaviour and ultimately lead to intergroup conflict, the concept of social identity is often presented as a group membership that needs to be avoided [62]. Conversely, social identity theories also highlight the nuance that one not only needs an identity [63,64], but also a sense of belonging to a positively valued group [65]. Along these lines, our analyses show that we should inquire into the more abstract and transversal identities that connect people, such as the identification with Brussels.
A second parallel we can therefore involve is, "feeling attached to or identifying with the social entity (a group, region, country)" [9] (p. 13). Nevertheless, we assessed that many of the participants' friendships are subject to unwritten rules, notably, silencing and avoiding particular topics. One reason is to divert the attention away from different topics as a coping strategy to deal with and to protect their ethnically diverse friendships, but also to prevent segregation among their peers and to avoid any escalation in the classrooms. In contrast, half of the respondents expressed being keen to discuss controversies on a regular basis with their classmates and teachers in the classroom. Some believe that "the more you hold back, the harder you react afterwards" (Respondent 31), whereas others believe that speaking openly in the classroom would create more tensions (Respondent 27). Schiefer and van der Noll [9] attribute the "acceptance of the social order and the compliance with social rules and norms" (p. 15) as idioms toward the common good.
A third parallel that we can draw is that controversial subjects are related to the common good and the social order, such as Charlie Hebdo and the Mohammed cartoons or LGTBQ rights. Taking this into consideration, controversial topics regarding freedom of speech and a positive attitude toward the limitation of Charlie Hebdo's cartoons might expose adolescents' inadequate knowledge of the legal meaning of freedom of speech and its history in European democracies. Our findings show that more in-depth research regarding the transfer of beliefs, views and perceptions among adolescents, as well as between adolescents and teachers, is needed, particularly with regard to how these transfers affect adolescents' ideas regarding the separation between religion and state.
In addition, various identity-related controversies were recounted by respondents of Moroccan origin whose intragroup peers are inclined to criticise them on religious or cultural matters. As such, our findings corroborate Mastari and Spruyt's [66] hypothesis, which argues that adolescents in an urban context with a collectivistic culture might experience constraints to bridging with adolescents from another ethnic origin. Along these lines, we highlight the necessity of further research to grasp how these beliefs and views are related to what [67] defines as the hierarchy of adolescents' values within a collectivistic and religious group system. The authors describe that while humankind mostly shares the same universal values, the hierarchy of these values might differ from culture to culture. Whereas 'religion' might be on the top of the hierarchy in collectivistic cultures, it might be at the bottom in more individualistic cultures. Another reason could be that these adolescents are ostensibly not empowered by the educational system in terms of approaching pitfalls. Notably, few dialogues are successfully facilitated among each other, with teachers nor even other institutes outside the educational system.
Due to their ethnic and cultural background, pupils with an immigrant background have a different political horizon (cf. [68]). We argue that some Brusselian adolescents have a broad geopolitical horizon. After all, the diversity of narratives these pupils encounter and hence bring to their classroom discussions [24,35] is not necessarily shared by Brussels' educational institutions. One respondent (6) depicted that during a visit to her family in Turkey, she witnessed the terroristic bombings of ISIS in Istanbul. She described that due to the silencing of ISIS victims outside of Belgium, she feels rejected by her school. During the interview she continuously expressed a feeling of resentment toward her school and Belgian society and had lost hope for a better future in Belgium. Likewise, one respondent's (28) geopolitical statements regarding ISIS caused stress among teachers and the principal, leading to the teachers dubbing him "a potential Syria fighter". After this event, the respondent felt stigmatised and avoided further conversations to prevent being targeted by the school and the police. As a result, he distrusts official institutions and is very doubtful about his future. Pelleriaux [69] describes this feeling of losing hope for a better future as a feeling of futility or social demotion. Similarly, van den Bos' [70] vertical deprivation states that feeling abandoned by the authorities might go hand in hand with feelings of unfairness.
Overall, students refraining from discussions about controversial topics and events could, however, be detrimental to their notions of citizenship [25,71]. The latter may also explain the mismatch identified by Mansoury Babhoutak and colleagues [72] between the ambitions of the education system and pupils' experiences of discrimination at school, especially since the latest Teaching and Learning International Survey (TALIS) shows that (Flemish) teachers rarely adapt their teaching to the ethnic diversity of their pupils [73].
In the aftermath of Brussels' terrorist attacks, all respondents expressed fear of the growing stigmatisation and discrimination of Muslims. Moreover, seven respondents expressed a severe lack of trust toward educational institutions, especially regarding racism and discrimination. This finding necessitates further research on how pupils as well as their teachers define racism and discrimination, and how both pupils and teachers interact in the classroom with respect to these issues.
Our findings highlight that further research is needed to inquire into the alleged mismatch between the (geo)political horizon of pupils and their teachers. We question how and where Brusselian adolescents will cope with this latent feeling of anxiety regarding discrimination and stigmatisation inside and outside the educational context after secondary school; will they be able to find constructive opportunities to interact with others about controversial topics in the future?
Prior research attests that Brussels' adolescents, despite their heterogeneity, strongly identify with their city as a social entity [74], and our study equally reflects this belongingness to Brussels. In contrast to Brussels, which functions as a centripetal dynamic, religion/philosophy, ethnicity/national loyalty and a geopolitical horizon all possess a centrifugal dynamic. These dynamics show that the four themes push each other out of balance. Furthermore, we detected processes of silencing, avoiding and voicing controversies [75], both between pupils and teachers, and among pupils in the classroom. As this research shows, Brusselian adolescents do not thus far experience teachers fostering open dialogues, nor do they see them approaching these subjects in any systematic matter. Respondent 9 mentioned that with regard to discussions, teachers facilitate in an abrupt manner: when discussions and dialogues in the classroom take place, they are quickly stifled, or they flounder, and everyone is ultimately "saved by the bell" (Respondent 9).
These findings show that neither ethnic diversity nor controversial topics de facto erode social cohesion: they neither foster social isolation nor 'bring out the turtle' [11] (p. 151) among the inquired adolescents. They curl up when they feel that classmates, teachers or principals do not take their socio-political ideas and grievances seriously. Therefore, we rationalise that feeling acknowledged through creating dialogue and discussions in the classroom might be a lever to catalyse belongingness and, as a consequence, foster social cohesion. Considering that conflict and cohesion are inherent in a pluralistic society [49], controversial topics should be discussed in a superdiverse classroom context. It is crucial to discuss adolescents' beliefs and grievances. Although teachers might be sceptical regarding adolescents' subjective feelings, they are real, as real as their behaviour and attitudes. Moreover, if schools want to empower their teachers and pupils, with respect to controversies, they should support and provide the framework for constructive dialogues, not to prevent conflicts from seemingly disappearing [76], but to prevent them from being destructive.

Conclusions
Thirty-four in-depth interviews with Brusselian adolescents allowed us to identify four themes between social cohesion and controversial topics: (1) Brussels, (2) religion and philosophy, (3) ethno-cultural or national loyalty and (4) political horizon. Whereas the first theme catalyses consensus, the latter three fuel conflict. We detected processes of avoidance, silencing and voicing between pupils and teachers, and among pupils in the classroom.
Although we feel confident that our results offer a good starting point for further research, as with all research, it is important to recognise that our study has some limitations. One of the main limitations of this research is the sample of respondents. It is relevant to mention that this research includes adolescents that were open to discussing and sharing their experiences, as there were several pupils who decided not to participate to the study for reasons of fear of recognition. Respondent 7, for example, stated that many of her class-and schoolmates refused to participate because they feared that this research was in collaboration with the police or the intelligence service. The pupils that participated, however, expressed enthusiasm regarding the fact that Brusselian adolescents are being heard and showed interest in the further proceeding of the research and its results.
To avoid a sample of respondents consisting solely of such enthusiastic pupils, for purposes of sample diversity we suggest making classroom observation an integral part of future research. Since it is not feasible to observe every class throughout the whole school year, and controversial topics most likely occur in specific subject classes, these observations should be arranged to take place when teachers introduce controversial subject matters during, for example 'civic education', 'biology' or 'history'. We emphasise the importance of observing not only pupils, but also how teachers handle controversies in the classroom. This is important to grasp potential differences between the worldviews of all actors involved in the classroom.
We hope that the findings of our interview-based study, which highlight the role of controversial topics in social cohesion processes, will help the understanding of the educational experiences of pupils and teachers further. Moreover, discussing controversial topics might be a pivotal point in promoting social cohesion in the educational context.
The Secretary General of the Council of Europe reinvigorated 'Civic Education' as a remedy against radicalisation and polarisation: 'In the long term, education policies and practices will be more decisive for tolerance and stability than any counter-terror measure, asylum reform or any new law.' [77]. In view of this, we strived to pave the way for the development of evidence-based methods for schools, teachers and their pupils regarding the use of controversial topics in the classroom to foster social cohesion among future generations of citizens.  Institutional Review Board Statement: At the time of this study, 2017-2018, the Vrije Universiteit Brussel, did not require ethical advice; however, the researchers followed the standard procedure by using for example an informed consent letter.
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author as consent was not obtained to publicise raw transcriptions.