Student teacher’s boundary experiences during an international teaching internship

Abstract A boundary is a metaphor for an experience of discontinuity wherein a socio-cultural difference is perceived as a challenge or obstacle in action or interaction. This case study explores eight student teachers’ perceptions of boundaries during an international teaching internship to identify where experiences of professional learning originate. We found four types of boundary experiences related to discontinuity: (1) existing pedagogical approaches, (2) personal aspects, (3) a specific school type or culture, and (4) the world outside the classroom. Results suggest that the learning potential of experiencing discontinuity resides in situations wherein student teachers’ beliefs are being questioned, thus making the student teacher aware of their implicit beliefs. Student teachers’ attempts to reposition themselves while experiencing discontinuity resulted in questioning their existing ways of thinking and acting. Everyday teaching approaches were no longer always taken for granted, thus opening alternate perspectives. In this study, student teacher experiences of discontinuity had various dimensions (cultural, professional, and personal), which also determined their learning potential.


PUBLIC INTEREST STATEMENT
The struggle caused by the encounter with something unfamiliar or unexpected can turn into a constructive stage of student' learning. This study reports on examples of such encounters during an international teaching internship when student teachers move between the (metaphorical) boundaries of disparate educational practices and cultures. We describe student teachers' perceptions of obstacles or challenges which they experience as discontinuity, exposing the roots of (potential) intercultural learning. Experiences of discontinuity captured situations wherein student teachers began to question their existing ways of thinking and acting. Everyday teaching approaches were no longer taken for granted, thus opening alternate perspectives. The student teachers began to understand that their own beliefs were not necessarily shared by others, as well as the value of the beliefs of others, thus raising an awareness of what they believe to be important in their teaching practices. For example in teaching strategies, or in teacher-student interaction.
When learning one's original culture, the entire surroundings, including family, community and institutions, support such efforts, and there is little discontinuity in what one already knows and what one is expected to learn. When learning a second culture, one comes into immediate conflict between the culture of the self and the new culture to which one is exposed. Reconciling these differences is critical to successful adjustment and subsequent learning. (Cushner, 2007, p. 37) Multiple studies have described the positive professional learning outcomes related to international experiences, such as building cultural awareness and sensitivity, and emphasizing how education abroad can be an important catalyst for student learning and development (Cushner & Mahon, 2002;Einfeld & Collins, 2008;Hammer, Bennett, & Wiseman, 2003;Marx & Moss, 2011;Zimmermann & Neyer, 2013). However, educators still have limited insight into how student teachers construct these understandings (Brindley, Quinn, & Morton, 2009;Tran, 2012), or how students' learning and development transpires during student teaching experiences abroad (Fee & Gray, 2013;Gleeson & Tait, 2012;Marx & Moss, 2011;Tan & Allan, 2010;Vande Berg, Paige, & Hemming Lou, 2012).
There are a small number of studies documenting how shared cultural understandings relate to individual interpretations (Malewski & Phillion, 2009;Trilokekar & Kukar, 2011) or taking into account that not all international experiences are beneficial (Gleeson & Tait, 2012;Savicki, 2010). In the field of teacher education, a limited body of empirical research exists about student teachers' experiences during international teaching internships, and how trainee teachers perceive its value for their own professional development (Tan & Allan, 2010).
Teacher educators who find it difficult to capture student teachers' professional learning during an international placement should contemplate paying more attention to instances when professional learning begins, rather than (positive) learning outcomes or overall effects (Biesta, 2014;English, 2013;Malewski & Phillion, 2009;Marginson, 2014;Selby, 2008;Walters, Garii, & Walters, 2009). Several studies have indicated that students abroad are being positioned in disequilibrium between disparate cultures or practices, and experience uncertainty and ambiguity, and both have learning potential (Akkerman & Bakker, 2011;Che, Spearman, & Manizade, 2009;Cushner, 2007;Malewski & Phillion, 2009;Marginson, 2014;Vanassche & Kelchtermans, 2014;Wenger, 2000). Schön (1987) has characterized such indeterminate, unexpected or problematic situations as the "swampy zones of practice". Dewey (1933Dewey ( , 1938 contended that experiences filled with confusion, perplexity, error, or frustration actually lay at the very core of learning. During an international teaching internship, student teachers become temporarily part of the traditions and values of an international school culture. This is an unfamiliar teaching context in which student teachers frequently have to (re)position themselves to find a (new) way of working that functions and feels "good" (Akkerman & Bakker, 2011;Biesta, 2014;Marginson, 2014).
A greater focus on student teachers' lived experiences, rather than just outcomes, is also salient since student teachers' professional development during teaching abroad has multiple dimensions (Gonzalez-Loureiro, Kiessling, & Dabic, 2015). An international teaching context can enhance various positive forms of professional and personal development (Cushner, 2007;De Grosbois, Kaethler, & Young, 2010;Pence & Macgillivray, 2008;Weber-Bosley, 2010), but may also result in discontent and distress (Gleeson & Tait, 2012;Savicki, 2010). According to Cushner (2007, p. 36), "the international lived experience sets the stage for developing a consciousness of multiple realities and serves as the stimulus that prompts new learning". The student' perspective is key for understanding how an international experience is gradually reflected in their development (Tan & Allan, 2010). Teacher educators who fix their attention on experiences of disequilibrium can gain a richer understanding of the students' professional learning, which can then in turn be used in teacher-training programs (Biesta, 2014;Cushner, 2007;English, 2013;Kelchtermans, 2009;Korthagen, 2017).
The main aim of this case study was to explore student teachers' perceptions of instances of disequilibrium to expose experiences wherein the student teachers' professional learning originated.

Boundary experiences during an international teaching internship
This case study uses the theoretical concept of a boundary experience to describe international teaching experiences wherein student teachers feel they are positioned in disequilibrium between cultures and professional practices. The theory of boundary crossing (Akkerman & Bakker, 2011;Akkerman & Bakker, 2012;Engeström, Engeström, & Kärkkäinen, 1995;Tsui & Law, 2007) uses the metaphor of a boundary to describe experiences whenin professionals are positioned in disequilibrium between various practices. Akkerman and Bakker (2011, p. 133;Akkerman & Bakker, 2012, p. 10) define a boundary as "a socio-cultural difference between different practices, or cultures, which is perceived as an obstacle, or challenge, leading to discontinuity in action or interaction".
An international teaching experience offers several opportunities for studying boundary experiences. Educators generally expect that students situated in an unfamiliar international context find their existing beliefs and modes of action do not always function, and these socio-cultural differences can enhance student teachers' professional development (Cushner & Brennan, 2007;Fives & Buehl, 2012;Marginson, 2014;Stachowski & Sparks, 2007). When studying boundary experiences, it is important to be aware of the unique nature of discontinuity, and to avoid focusing on overall outcomes or only culture (English, 2013). Student teachers are likely to experience socio-cultural differences while working in a new educational system and an unfamiliar school culture (Pence & Macgillivray, 2008;Zihou, Jindal-Snape, Topping, & Todman, 2008), living in an unknown culture (Jang & Kim, 2010;Zihou et al., 2008), or handling multiple socio-cultural differences without their existing social networks (Hendrickson, Rosen, & Kelly Aune, 2011;Montgomery, 2010).
When students perceive a socio-cultural difference as a boundary, this is the key experience of discontinuity. Discontinuities vary and may be experienced as transient, dramatic first-time, cyclical, or cumulative events (over time) (Zimbardo, 1999, p. 360). English (2013, p.114) describes discontinuity as physical, emotional, or existential moments in which an individual encounters something new or unfamiliar. This encounter disturbs the individual's planned or desired course. Whether a socio-cultural difference is experienced as discontinuity by student teachers or not is subjective, culturally and historically informed and context-dependent (Akkerman & Bakker, 2011;English, 2013). Student teachers who experience similar socio-cultural differences (for example, in classroom management) may or may not experience discontinuity. The value of experiencing discontinuity resides in the fact that the struggle caused by an encounter with something unfamiliar or unexpected can turn into a critical stage of learning, exploring, or experimenting as the individual attempts to bridge the worlds he or she lives and works in (English, 2013;Tsui & Law, 2007;Waitoller & Kozleski, 2013;Ward, Bochner, & Furnham, 2001).
Building bridges between disparate practices comes in various forms and shapes and generally compels an individual to self-reflect on the importance of negotiating contextual, social, and cultural meanings outside their familiar educational environment. These forms of intersubjectivity can inspire a co-construction of knowledge, or broaden the individual's professional repertoire (Akkerman & Bakker, 2011;Dooley & Villanueva, 2006;Finlay, 2008;Goodwin, 2010;Waitoller & Kozleski, 2013;Walker & Nocon, 2007). Attempts to bridge other worlds and practices are defined as boundary crossings (Akkerman & Bakker, 2011;Tsui & Law, 2007). In intercultural studies, the process of bridging cultures is usually described as a cultural adjustment or adaptation to the new culture (Hofstede & Hofstede, 2005;Ward et al., 2001).
In this case study, we explore the various types of boundaries perceived by eight student teachers during their international teaching internships, and in which their professional learning is (potentially) rooted.

Data collection and participants
This study is designed as a qualitative, small-scale case study using an interpretative research approach (Borko, Whitcomb, & Byrnes, 2008;Smith, Flower, & Larkin, 2009) to understand boundaries perceived by student teachers in internships abroad. Borko et al. (2008Borko et al. ( , p. 1025) describe how interpretative research "seeks to perceive, describe, analyze, and interpret a specific situation or context, preserving its complexity and communicating the perspectives of the actual participants". Participants in this study include eight student teachers from a post-graduate teacher education program at a Dutch university. The student teachers were all Dutch natives, except one student who had been born in South Africa and moved to the Netherlands at age10.
The participants were approached to participate based on the variety of their study abroad destinations and teaching subjects (History, English, and Geography). All gave their consent to participate. This teacher education program was selected because it has a specific focus on international education and includes an international internship. The program is taught in English and specific attention is paid to intercultural competencies and pre-departure preparation. Apart from the regular teacher-training program, this program offers two integrated modules that focus on topics related to content and language-integrated learning and international and crosscultural education. Examples of topics are theories related to teaching a subject in English and how to raise pupils' cultural awareness. Student teachers in the program participate in two teaching internships: the first in the Netherlands at an international school (with an International Baccalaureate Diploma Program) or a bilingual school and teach in English, and the second at a secondary school abroad. Our study focuses on the second, international internship when the student teachers are abroad for 3 months teaching in regular secondary schools in the UK, Norway, or St. Martin, or a girls' school in South Africa, or a boarding school in the UK. Individual data collection was conducted from December 2013 until June 2014.

Data sources
Four data sources were created and consulted. These included a personal biography of each student teacher, two individual inventories of perceptions of socio-cultural differences and individual interviews. Before departure, each student teacher wrote a personal biography describing their social backgrounds, educational careers, international experiences, and affiliation with various themes related to internationalization (e.g. world citizenship) and expectations. Student teachers completed a questionnaire on perceived professional and personal socio-cultural differences they noticed while abroad in the first and third month of their internships). Finally, each student teacher was individually interviewed upon return from abroad using a semi-structured interview guide to explore socio-cultural differences and experiences of discontinuity. All student teachers checked and verified their individual transcripts of these interviews.

Data analysis
In this study, a boundary was defined as a problematic or challenging socio-cultural difference leading to discontinuity in action or interaction (Akkerman & Bakker, 2011;Akkerman & Bakker, 2012). Based on participants' self-reporting, we identified and constructed the perceived boundaries the student teachers described in their narratives. The boundaries the eight participants described were analyzed using a narrative inquiry approach (Connelly & Clandinin, 1999).
Individual data sources were analyzed in several rounds using NVIVO for open and axial coding (Boeije, 2010;Corbin & Strauss, 2008). The first round of coding focused on identifying the individual socio-cultural differences and similarities the student teachers described, which resulted in six thematic coding categories: teaching aspects, interpersonal interaction, intrapersonal aspects, school culture, cultural aspects, and social-economic aspects. All codes were crosschecked with the student teachers' individual biographies to establish whether or not those themes had also played a role in their teaching before their stay abroad.
Next, the instances of discontinuity that student teachers described in their interviews and inquiries were examined to categorize the socio-cultural differences they had perceived as an obstacle or challenge. We determined whether or not the student teachers perceived a sociocultural difference as a boundary by: (1) examining if the same socio-cultural difference reoccurred in distinct data sets (indicating that the problematic difference occurred during and after the internship), (2) examining the student teachers' discourse when they discussed sociocultural differences, (3) constructing whether or not socio-cultural differences were interrelated in a critical incident, and (4) examining the student teachers' responses to socio-cultural differences. Based on the analysis (Table 1), 15 boundary experiences were constructed.
An audit trail procedure (Akkerman, Admiraal, Brekelmans, & Oost, 2008) was used to examine the analytic choices of identifying boundaries for validation of the research approach in general. The three generic criteria of the audit trail were visibility, comprehensibility, and acceptability. The main points of discussion in the audit trail report addressed the methodological choices for identifying boundaries, as well as the theoretical question of whether or not all boundaries were necessarily problematic and/or challenging. The results of the audit trail were used in the final data analysis.

Results
This case study uses the theoretical concept of a boundary experience (Engeström et al., 1995;Tsui & Law, 2007) to describe international teaching experiences wherein student teachers experience discontinuity when they feel they are positioned in a disequilibrium between cultures and professional practices (Akkerman & Bakker, 2011;English, 2013;Marginson, 2014). In this section, we present the results of the student teachers' personal biographies, individual inventories (two) of perceptions of socio-cultural differences, and individual interviews. In the discussion section that follows, we engage with findings from relevant literature on student teachers' international and boundary experiences.
The exploration of the student teachers' experiences of discontinuity during an international teaching internship resulted in the construction of 15 boundaries displayed in Table 2. The student teachers' verbal and written statements described various professional or personal situations that at first sight appeared to be similar, however, one student teacher may have perceived the situation as a boundary, while another did not. A total of 13 boundaries were unique experiences. Two boundaries, regarding teacher-pupil interaction and expectations of the role of a teacher (Table 2: #1 and 7), were perceived by more than one participant. This can be explained by the fact that two student teachers taught in the same school and apparently perceived the socio-cultural difference in a similar way.
We found 12 boundaries that the student teachers perceived as (negative) obstacles, and 3 boundaries the participants perceived as a (positive) challenge. Whether the student teacher perceived a boundary as an obstacle or challenge made a difference in how they experienced discontinuity.
In the 12 boundary experiences the participants perceived as an obstacle, their written and verbal statements described situations wherein they struggled to find a position that "worked". In most boundary experiences, this struggle lasted throughout their internship. Some boundary experiences lasted a few weeks (e.g. Table 2: # 11), wherein a student struggled with a language barrier. Some perceived obstacles were rather extreme, such as domestic violence or a pupil's suicide (Table 2: # 3, 6 and 7). The student teachers' reflections were often focused on the present. What most of the boundary experiences had in common was the fact that clear-cut solutions for the obstacles rarely existed. The student teachers' struggle with boundaries triggered a key question: "To what extent do I want to adapt or reposition, in order to handle the obstacle?" This question forced the participants to think about existing professional or personal beliefs they valued.
Three examples of boundaries originated from positively challenging experiences. Although the three boundary experiences were positive, the boundary still pre-occupied the student teachers Table 2. Boundaries perceived by student teacher(s) during an international teaching internship including negative obstacles and positive challenges a Negative boundary obstacles perceived by student teachers 1 How pupils and mentors are accustomed to teacher-centered activities, including a power distance between teacher and pupils 2 The fact that she teaches in a school where many pupils have a socio-economic background different from hers, including poverty (affecting their behavior at school and perspective on life)  during most of their internships and also motivated them to think about their position in negotiating disparate cultures and practices. In contrast to the obstacles, the student teachers' reflections on challenging boundaries were also future oriented. The student teachers described how the challenge inspired them in their professional lives, felt rewarding and made them aware of possible future ambitions.

Types of boundary experiences
For the 15 boundaries (Table 2), four types of boundary experiences can be distinguished wherein the student teachers' professional learning is (potentially) rooted: (1) Discontinuity is related to existing pedagogical approaches and student teachers perceive boundaries in teaching aspects (#1 and 14).
(2) Discontinuity is related to personal aspects. Student teachers perceive boundaries of a personal nature reflected in their private life, or their teaching practice (#4, 5, 10, 11, 12, and 15).
(3) Discontinuity is related to specific school type or culture. Students perceive a boundary in their teaching practice, which is the result of the school culture or school type of the school where they are interning (#7, 8, and 9).
(4) Discontinuity is related to the world outside the classroom. Student teachers perceive a boundary where the local socio-cultural context influences their profession or teaching practice (#2, 3, 6, and 13).
We now describe each of the four types of boundary experiences and provide examples.

Boundary experiences wherein discontinuity related to existing pedagogical approaches matters
The two boundary experiences (Table 2) explicating discontinuity in existing pedagogical approaches concerned teacher-pupil interaction. We found one example of an obstacle (#1), and one example of a positive challenge (#14). We highlight both cases to compare an obstacle and challenge in a similar teaching aspect.
The boundary perceived as an obstacle (#1) was described by three participants teaching in the same South African school. The discontinuity that the student teachers described was caused by the fact that they experienced a sharp contrast in pedagogical approaches. In the internship school, a teacher-centered pedagogy was expected from teachers, while the Dutch student teachers were generally trained to teach in a student-centered way. The problematic interaction with pupils further enhanced the student teachers' experiences of discontinuity. Pupils were accustomed to teacher-centered classes and did not always respond well to the student teachers' attempts to incorporate some student-centered activities in their lessons.
One of the participants, Suzanne, perceived the teaching methods she used at school as problematic, sometimes even irresponsible, compared to the ones she had been taught in her teacher-training program.
I experienced difficulties with teaching pedagogy. I believe that in-depth knowledge and student-centered activities are important (. . .) In South Africa that type of teacher is almost "not done". The teacher is in charge, gives a monologue, and the pupils start working on the assignments. That's a way of working I cannot relate to (. . .) and something I found really difficult. I could organize student-centered activities, but that would get me into problems, because I would lag behind in the overall curriculum planning.
The student teachers made individual attempts to find their position in the disequilibrium of the disparate teaching approaches. Although it appeared to be a struggle that could not really be solved, the importance of the experience of discontinuity resided in the fact that it raised an awareness of the value of an existing professional belief. Although Suzanne still valued her existing pedagogical approach, her position moved to an understanding that in another context, alternative teaching approaches are also valuable.
Pupils from different cultures, learn differently and have different learning strategies. A teaching strategy that was taught to them. South African pupils can listen really well, compared to Dutch pupils. In the Netherlands you have to offer various teaching activities to make pupils work (. . .) In South Africa pupils like to listen to long stories and prefer teachercentered activities. I have learned to appreciate that as well.
In another boundary experience (#14), Simone had almost the opposite experience at her Norwegian school compared to Suzanne in South Africa. Simone described how the apparent lack of authority and power distance at her school was rather confusing at first, especially because she expected this pedagogical approach to be problematic. I thought that I would have a lot of difficulty in teaching in Norway, because I am very direct. In the Netherlands I had quite an authoritarian teaching approach. My mentor literally said: "you have to prepare yourself on this teaching aspect, because they are very different down there".
Simone perceived a boundary in Norwegian teaching pedagogy. Pedagogy proved to be a key issue during her internship, but in a positive way. In Norway, teacher-student interactions are very informal and with little hierarchy. In the beginning, this felt a bit awkward when Simone had to find her position. For example: . . . when you want to change something in the curriculum, you always have to consult the pupils (. . .) In the Netherlands you can just decide to give an extra test, that's not allowed here. In Norway, when you want to take some more time to discuss the Cold War, instead of discussing European integration, you definitely have to ask permission.
Simone's perception of this boundary soon changed from surprise and puzzlement toward being inspired by the alternative pedagogical approach.
It's like dealing with a brother or sister, very informal, but pupils still respect you. I really appreciated this way of working (. . .) The Norwegian way of teaching was not that different from the Dutch way, but it was just something I wasn't used to in teaching (. . .) I started to focus more on the pupils instead of me. I wasn't so pre-occupied anymore with how I stood, or what I did, but rather whether pupils had understood what we discussed (. . .) It made me wonder: "have I played a role during my first internship in the Netherlands? What was it that made me teach that way?"

Boundary experiences wherein discontinuity related to personal aspects matters
In the boundary experiences (Table 2), where discontinuity in personal aspects mattered, student teachers' character (#4 and 10), biography (#5), emotions (#11 and 12), or ambitions (#15) determined their perception of a boundary during their teaching internship. The personal nature of the boundary experiences often made the experiences more intense.
Discontinuity made the participants aware of the thin line between their personal and professional lives. For example, Suzanne (with a bi-cultural background), found that personal values, such as humility and respect, although not necessarily valued in the Netherlands, were important and valued in South Africa. Suzanne struggled with how to find her position between disparate values during her internship.
The more personal nature of the boundary experience also made it more difficult to share the obstacle or challenge with others. This was especially problematic in an international context wherein the students had to operate without their familiar social network. Ellen specifically addressed this problem in her boundary experience (#4).
Personal boundary experiences can trigger stronger emotions. For example, Simone felt isolated for weeks because her Norwegian colleagues refuse to speak English with her. She felt especially frustrated, because she had participated on her own initiative in a pre-departure training including a Norwegian language course. Simone felt like an outsider and perceived her experience as a culture shock. Janet's boundary experience (#12) described how she found it difficult to be constantly on her guard because of safety issues in South Africa. Janet felt she had to be careful at all times, plan ahead and depend on travelling with others. This particular boundary experience was different from the others because it was not determined by the school context. Paula experienced discontinuity wherein personal aspects mattered because her personal outlooks on life clashed with a difference in life perceptions in the Caribbean. She described how she was well-organized and liked to plan ahead. Paula struggled upon arrival with the fact that not everything in the Caribbean is planned, and people don't always keep promises. This struggle was also reflected at school.
I had a problem in adapting to this attitude at St. Martin of "what can't be done today, will be done tomorrow" (. . .) It was really difficult for me, because that's not how I am. For example, I had to prepare my lesson materials way ahead, because as a teacher you were not allowed to make your own copies, which was a task of the caretaker. The problem was that it could take a day, but it could also take five days.
Paula described how she struggled with this discontinuity, which appeared in various shapes and forms throughout her internship. She knew that the discontinuity she experienced was mainly caused by her character and expectations, while she simultaneously understood that she had to make some adaptations.

Boundary experiences wherein discontinuity related to a specific school type or culture matters
We found three boundary experiences wherein discontinuity in a specific school type or culture matters (#7, 8, and 9). This type of boundary experience was caused by experiences of discontinuity wherein student teachers faced an unfamiliar school culture, or because they taught in a special school setting such as a boarding school or a girls' school. Three boundary experiences (#2, 8, and 9) occurred at a South African girl's school, with strict rules and regulations about what was expected from teachers as well as students. Marc's boundary experience (#8) was somewhat unique, because he described how teaching at this girls' school as a male teacher caused additional obstacles in his interactions with female pupils. Ellen and Adriana describe a similar boundary experience (#7) because they taught at a boarding school. Both students and staff resided at the school complex, which had an effect on teachers being available at all times, and how teachers and pupils interact.
From the start of her internship, Janet was shocked by the number of rules in her South African school.
We received a booklet with all the school rules that applied to teachers (. . .) I was so afraid to do things wrong, because there were so many rules (. . .) In the Netherlands you also have different types of rules, but most of them are not written down. In South Africa there were rules how you have to look like, how to dress, what you can and can't do, and so on (. . .) That was my first culture shock where I thought: "I am not sure if I'm fit for this, or whether I will persevere". Janet gradually understood that the discontinuity she experienced was more than rules, the broader context was hierarchy and power distance.
There was a clear hierarchy in the school, between pupils and teachers, but also between beginning and experienced teachers. (. . .) There were, for example, court yards in the school, where teachers were allowed to walk and pupils were not (. . .) On the very first day, all students interning were assigned to a specific table in the teachers' room. It turned out to be the table we were expected to sit during the whole internship (. . .) One funny example. We wanted to drink a cup of tea. My fellow student [teacher] just picked a few cups. A teacher said: "No, no, no! Those cups are from the head mistress, you are not allowed to use those!" Janet described how she tried to position herself in this school culture during her internship: I was very careful (. . .) I also checked with colleagues what was allowed (. . .) I think it took about one and half month when I thought: "I think I get it" (. . .) I noticed for example that not all teachers precisely dressed according to the rules (. . .) I discovered that not everything was as strict as what was written down (. . .) You get sort of used to it.

Boundary experiences wherein discontinuity in the world outside the classroom matters
The student teachers described four boundaries wherein the outside world had an influence on participants' experiences of discontinuity within the classroom. In four boundary experiences (#2, 3, 6, and 13), the students experienced discontinuity in how pupils' domestic situations had influence in the classroom. Pupils' problematic domestic situations were caused by the local socio-economic context. For example, Amy taught in a relatively poor area in the UK with high unemployment rates. The difficult socio-economic context was reflected in various aspects within the school, such as an emphasis on child safeguarding. This context demanded a new position from Amy, who needed to be more than a subject teacher for her pupils (#2). In the other boundary experience (#3), Paula found her pupils' behavior in the classroom problematic for her teaching. She found that some of her pupils suffered from families with a divorce and domestic violence. She understood that this was a type of discontinuity she could not really solve, but also raised an awareness of the importance of pupil's domestic situations. Janet perceived a boundary experience (#6) at her South African school when one of her pupils suffered from domestic violence. Janet's experience of discontinuity went beyond domestic violence and addressed a key belief-teachers have a responsibility to protect students. Janet's position was that the school had to talk with the parents, while her South African colleagues argued that teachers should not intervene in domestic situations.
During one of his trips abroad, Marc visited an orphanage school in a South African township that was successfully run by volunteers.
We visited a school in Soweto for children without parents, or at least their parents couldn't take care of them. Those children are left behind (. . .) At first you think as a teacher: "This is something I can use during my lessons" (. . .) There's so much bad publicity on various development projects, that it doesn't work, or that people are made dependent of this help (. . .) This experience showed me that such small-scaled projects work.
Marc's boundary experience (#13) proved to be an intense and confronting situation, which did not influence his internship at the time, but instead went beyond his boundary experience.
You observe the circumstances in a country such as South Africa, with its polarization, inequality, poverty and racism (. . ..) that makes quite an impression (. . .) Sometimes you experience something, for example, a concert which you attend and then it makes a temporary impression. You think about it for a few days and that's it. But sometimes an experience really hits you (. . .) and you think that this an experience which can have some meaning later on in your life (. . .) The boundary experience challenged Marc to think about the teacher he wanted to become as well as the possible consequences for his private life.

Discussion
In this case study, we described and analyzed 15 boundary experiences (Table 2), eight Dutch student teachers described during their international teaching internships to expose the roots of (potential) professional learning. We categorized the boundary experiences into four groups of discontinuity: (1) existing pedagogical approaches and teaching aspects, (2) personal aspects, (3) specific school type or culture, and (4) the world outside the classroom. English (2013, p.114) describes discontinuity as physical, emotional, or existential moments that disturb an individual's planned or desired course. Our findings reflected English's descriptions of discontinuity, e.g. discontinuity when encountering a teacher-centered pedagogy in South Africa versus the student-centered pedagogy the Dutch student teachers had learned (boundary experience 1), or discontinuity in how pupils' domestic situations had influence in the classroom (#2, 3, 6, and 13). As we expected beforehand, the fact that the student teachers were positioned in disequilibrium between disparate cultures and practices evoked situations wherein the student teachers experienced discontinuity, which has also been addressed by Akkerman & Bakker (2011), Malewski and Phillion (2009), Marginson (2014), and Wenger (2000. The examples of boundaries we found frequently led to unclear, temporary, or indeterminate endings, as Schön (1983Schön ( , 1987) has highlighted, which can occur in student teacher's international internships. An example from our findings is the boundary (#5) that Suzanne perceived when she struggled to find a position between the culture she was raised in (Dutch) and the culture of her ethnicity (South African) during her internship in South Africa. We found several examples of situations wherein an international teaching experience made the student teachers begin to question either their existing ways of working and thinking, or that of their colleagues in the internship schools. Such questioning is an important aspect of discontinuity (English, 2013), which in this study resulted in student teachers' attempts to find a (new) position in the disequilibrium. The student teachers' (re)positioning can be an important beginning of their professional learning at the beginning of the co-construction of their professional knowledge as mentioned by Akkerman and Bakker (2011), Pence and Macgillivray (2008), and Tan and Allan (2010), or in raising an awareness of what they believe to be important in their teaching practices as discussed by Beauchamp and Thomas (2011), Biesta (2014), and Marginson (2014).
The constructed boundary experiences can provide teacher educators with insight into sources of the student teachers' beliefs (Levin & He, 2008;Cuadra-Martínez, Castro, Vystrcilová, & Jancic-Mogliacci, 2017). The student teachers' perception of a boundary begins during situations wherein they encounter something new or unfamiliar (Akkerman & Bakker, 2011;English, 2013;Malewski & Phillion, 2009;Marginson, 2014) and experience it as discontinuity and their beliefs are being addressed in a positive or negative way. In various boundary experiences, personal aspects (e.g. character, personal biographies, or upbringing) were influential when the student teachers were questioning their beliefs, e.g. a boundary (#10) where Paula (well-organized, likes to plan ahead) begins to understand how flexibility is an important asset as a teacher when she experiences discontinuity in the Caribbean where not everything is well-organized. An international teaching internship also encourages cross-cultural comparisons and appears to make student teachers' implicit beliefs explicit (Brindley et al., 2009;Marx & Moss, 2011;Pence & Macgillivray, 2008). When a cross-cultural perspective occurs, student teachers begin to understand that their own beliefs are not necessarily shared by others and the beliefs of others can be valuable as well (Cushner, 2007, p. 33). Cushner's work is reflected in our findings from Simone and Marc, for example, who spoke about the value of the type of pedagogy used by local teachers (Simone, #11), or a voluntary project in Soweto that shows how education can be valuable in various shapes and forms (Marc, #13). The value of such reflections on boundaries resides in the fact that the student teachers started to think about where they stood or who they were as teachers, which has been addressed by Beauchamp and Thomas (2011). The student teachers did not always take for granted the small, plain or everyday teaching details such as teaching methods and pupil interaction in their unfamiliar cross-cultural setting. This particular finding, as illustrated by Janet's boundary experience (#1) in South Africa and Paula's boundary experience (#10) in St. Martin, explains the subjective nature of boundary experiences and the fact that similar socio-cultural differences can be perceived in various ways by student teachers (Akkerman & Bakker, 2011;English, 2013;Savicki, 2010).

Conclusion
This study shows that educators who are interested in the origin of student teachers' professional learning during international teaching internships, should focus on student teachers' (re)positioning during problematic or challenging situations. The findings of this study confirm that educators who want to capture student teachers' professional learning when experiencing discontinuity while teaching abroad need to be aware that discontinuity has multiple dimensions (cultural, professional, and personal aspects) and should not focus only on discontinuity in teaching knowledge or skills (Biesta, Priestley, & Robinson, 2015;Gonzalez-Loureiro et al., 2015;Trilokekar & Kukar, 2011). The multiple dimensions of discontinuity appear to determine how student teachers perceive challenges or obstacles, and how this intersubjectivity results in their (re)positioning between various practices as discussed by Beauchamp and Thomas (2011) and Tsui and Law (2007). The student teachers' descriptions of how they struggled with (re)positioning during experiences of discontinuity indicate that learning potential appears to be present during (re)positioning between disparate cultures and practices, which is in line with findings from Bakker (2011), English (2013), Killick (2012), and Lave and Wenger (1991).

Future implications
Teacher educators who are interested in student teacher development after experiencing discontinuity also need to understand when student teachers are able to renegotiate a boundary and create continuity from the discontinuity they have experienced during an international teaching internship (Akkerman & Meijer, 2011;English, 2013) and when they cannot. Insights into experiences of student teachers' repositioning between states of (dis)continuity can provide teacher educators with a richer understanding of student teachers' professional development (Akkerman & Bakker, 2011;Tsui & Law, 2007;Walker & Nocon, 2007). Student teachers' positioning after experiences of discontinuity can help teacher educators in the critical examination of student teachers' practices, including their aversions or persistent beliefs (English, 2013;Vanassche & Kelchtermans, 2014, p. 126). English (2013) emphasizes that the opening created by the interruption of discontinuity becomes truly significant, when a teacher is not only able to reflect upon the experience of discontinuity itself, but also when the teacher is able to place the experience within the context of previous experiences or prior knowledge. Educators who want to have a richer understanding of when an experience of discontinuity matters for beginning teachers' professional development have to consider taking an ecological perspective on student teachers' professional development (Biesta et al., 2015;Mishra & Koehler, 2006). An ecological perspective takes past, present, and future dimensions into account (Dewey, 1938;Goodman, 1988;Kelchtermans, 2009). We suggest that teacher educators need more understanding of the role their student teachers' personal histories and interpretations play (Goodson, 1984;Kelchtermans, 2009) during boundary crossings.
We also found the theory of boundary crossing (Akkerman & Bakker, 2011;Engeström et al., 1995) was of additional value for educators interested in an ecological approach for understanding student teachers' professional development in a cross-cultural context. The concept of a boundary experience (Akkerman & Bakker, 2011;Tsui & Law, 2007) goes beyond individual attempts to reconcile or overcome cultural differences, or the notion of cultural adaptation (Berry, 1999;Ward & Chang, 1997;Ward & Kennedy, 1999). By taking various dimensions of student teachers' experiences into account, including professional, personal, and cultural aspects, educators can further understand the complexity of teaching abroad (Chirkov, 2009;Marginson, 2014;Trilokekar & Kukar, 2011). This approach can also help educators capture how personal, professional, or cultural dimensions are intertwined in student teachers' professional development (Gonzalez-Loureiro et al., 2015).