Developing 21st century teaching skills: A case study of teaching and learning through project-based curriculum

Abstract This study investigated secondary school teacher’s experiences in learning to teach 21st Century skills through the design and implementation of Project based (PBL) curriculum. Data collection focused on in-service teachers who completed a 3-unit, 16-week course part of a Master’s degree program in Curriculum & Instruction (C & I). Data were collected through two pre-post surveys—one measuring knowledge and the other measuring teachers’ confidence in integrating PBL units into the curriculum, and post course interviews. Results revealed that using PBL as an integrated teaching and learning strategy in the preparation of teachers can develop the self-efficacy required to support the curricular demands necessary to address the learning needs of students for the 21st Century. A sustained focus on pedagogy, curriculum, and skill acquisition is critical to developing 21st-century teaching skills. Implications for teacher learning and the importance of engaging teachers in a professional development experience that integrates college and career readiness curricula and PBL methods are also discussed.


Introduction
An increasingly complex society and a rapidly changing technology-based economy have posed new and demanding challenges to schools and communities alike. School systems worldwide are being asked to develop frameworks emphasizing developing the skills, knowledge, and attitudes necessary for success in the 21st Century. In the United States, for example, employers and policymakers alike have argued that America's high schools are not "producing the twenty-firstcentury graduates needed to compete and succeed after high school in an increasingly complex and interconnected world" (Achieve, 2010, p. 7). In response, the National Governors Association released a new set of academic standards, the Common Core Standards (Common Core State Standards Initiative, 2010). The Common Core State Standards (CCSS) provide guidelines desiged to ensure students are prepared for entry-level careers adn/or college level courses. Such, indicators of readiness include complettion of a college preparatory curriculum, standardized test scores, and career-related skills. However, other factors such as critical thinking, problem-solving, creativity, collaboration, communication, digital and technological literacy can also be important determinants of success in college and careers (Conley 2007;Dweck, Walton & Cohen 2011;Schleicher, 2012;Wurdinger & Rudolph, 2009).
In a report by Achieve.org (Achieve, 2016), there is ample evidence that too many young people in our American education system graduate from high school poorly prepared for college, careers, and the military. The report recommends that every state adopt college and careerready policies to ensure students graduate academically prepared to enter the workforce and post-secondary education. A preferred approach in districts across the U.S. has been careerthemed programs of study that combine standards-based academic and career and technical education (CTE) content. Often referred to as college and career academies, these high schools provide a college preparatory curriculum, rigorous career education, work-based experiences, including job shadowing, internships, counseling, and other supports. The fundamental goal is to increase post-secondary opportunities for all students, particularly students from diverse income, race, ethnic, language backgrounds, or disability status (Rustique & Stam, 2013;Stern et al., 2010). However, improving high school outcomes and addressing the demands of a global economy requires that education systems increase the supply of teachers with strong working knowledge of their content and the pedagogical techniques necessary to link their content with real-world application. Researchers and practitioners agree that building an education system with "powerful learning focused on the demands of life, work, and citizenship in the 21st century" requires a strong human capital base (Darling-Hammond & Oakes, 2019, p. 1). In other words, preparing teachers to teach 21 st Century skills must focus on the curricular demands necessary to address the learning needs of students for the 21 st Century (Bell, 2010;Brears et al., 2008;Mioduser & Betzer, 2007;Schleicher, 2012). Rustique and Stam (2013) argue that both aspiring and experienced teachers would benefit from learning opportunities that focus on 1) performance-based curriculum to demonstrate attainment of content knowledge and college and career readiness skills, and 2) curriculum design that differentiates and scaffolds instruction for diverse learners (p. 8). While no research specifically addresses the preparation of teachers for the large-scale transformation called for in the college and career readiness reform movement, Warner and colleagues (Warner et al., 2015) evaluated the use of project-based learning units that alignwith core elements of college readiness, including integration across content area courses, work-based learning experiences, and use of common assessment rubrics. Researchers concluded that teacher teams with a high level of support in the design of course curriculum, project-based learning units, and assessment rubrics were critical to ensuring the overall quality of instruction, teacher knowledge, and capacity (Warner et al., 2015).
In the United States and around the world, teacher training programs have transformed the way educators connect academic learning with technical skills and real-world applications (Farnan et al., 2014;Hemker et al., 2017;De Simone, 2014). Such programs focus on integrating learning experiences students need to demonstrate college preparation, career development, and active citizenry leading to productive and prosperous 21 st Century lives (Farnan et al., 2014;De Simone, 2014). This study investigated secondary school teacher's experiences in learning to teach 21 st Century skills by designing and implementing PBL curricula. The researcher in this study integrated Project-based curriculum design principles into a University-based graduate program for secondary school educators. This paper, describes teachers' professional learning experiences in a graduatelevel course focused on developing 21 st Century teaching skills. This study had three research questions: (1) What is the impact of a 3-unit graduate-level course on teachers' knowledge of PBL curriculum design?
(2) What is the impact of a 3-unit graduate-level course on teachers' confidence in designing PBL units?
(3) How do teachers perceive PBL curriculum design in relation to the development of students 21 st Century skills?

Project-based learning
Project-Based Learning (PBL) prepares students for academic, personal, and career success and readies young people to rise to the challenges of their lives and the world they will inherit (PBL Works, 2019). This study applies the following definition: PBL is a teaching method in which students gain knowledge and skills by working for an extended period of time to investigate and respond to an authentic, engaging, and complex question, problem, or challenge (PBL Works, n.d., para. 3). In PBL, the project is central to the curriculum and a core teaching strategy through which concepts, content, and standards are taught. Projects are focused on questions or problems in which students make connections between activities, principles of a discipline, and the underlying conceptual knowledge (Grant, 2002;Parker et al., 2011). In addition, projects embody characteristics of authenticity with real-life challenges that offer solutions with the potential to be implemented (Barell, 2007;Barron & Darling-Hammond, 2008;Boss & Krauss, 2007;Larmer & Mergendoller, 2015).
Researchers and practitioners suggest that PBL has the potential to reach the cognitive processing levels necessary for 21st Century college and careers (Association for Supervision and Curriculum Development (ASCD), 2012; Barron & Darling-Hammond, 2008;Boss & Krauss, 2007;Boss et al., 2011;Ross, 2012). Secondary school teachers who use PBL in their classrooms have the potential to increase student engagement and motivation while at the same time providing rigorous academic content combined with real-world applications of that knowledge in a particular industry sector. While some literature provides an examination of integrated projects "as an indicator of the rigor of teaching and learning" (Warner et al., 2015, p. 31), little is known about the effectiveness of this approach in career-themed academies. Moreover, no research describes how teachers design and implement such projects. The available research focuses on PBL as a tool to engage students in real-world tasks that cross over into all areas of academic content. However, it may not necessarily apply to an industry theme. With a growing emphasis on schools providing a career-themed college-preparatory curriculum that prepares students to identify and solve problems, the idea of engaging teachers in PBL practices that foster depth of learning and engage students on a personal level is quite appealing.
The number of PBL studies involving teacher candidates at the higher education level is limited (Brears et al., 2008;Hartman et al., 2018;Hixson et al., 2012). However, evidence suggests that PBL can help both pre-service and in-service teachers better engage their students with content and pedagogy in a collaborative, technology-enhanced environment designed to foster student learning (Bhattacharyya & Bhattacharya, 2009;Ertmer et al., 2014). A case study of social studies teacher candidates analyzed the impact of problem-based learning and pedagogical devices that could guide students to gain the cognitive skills required to effectively address complex problems and issues (Wynn & Okie, 2017). In this study, researchers reported that teacher candidates felt confident about planning and implementing PBL and attributed that confidence to their experience with multiple PBL activities in the methods course (Wynn & Okie, 2017). Moreover, these candidates explicitly identified the potential power of PBL to improve the learning environment in contrast to the traditional learning environment that was common in their classrooms (Wynn & Okie, 2017). Similarly, Saye and Brush (2004) studied how to support teachers in implementing PBL in secondary social studies classrooms and found that modeling, scaffolding, and collaboration were effective in helping teachers utilize PBL.
The application of PBL as an integrated teaching and learning strategy in the preparation of teachers is believed to develop a level of self-efficacy required to support the curricular demands necessary to address the learning needs of students for the 21 st Century (Bell, 2010;Brears et al., 2008;Mioduser & Betzer, 2007;Wurdinger & Rudolph, 2009). Drawing on Grossman et al. (2009), the goal is to enable teachers to identify the core domains of college and career-based reform models and implement high leverage practices that can support the development and implementation of 21 st Century curricula. If you suppose education systems are to improve schools for the 21 st Century, then they must increase the supply of teachers with strong working knowledge of their content and the pedagogical techniques necessary to link their content with real-world application. Programs must be well-designed and provide a curricular focus on the following key concepts: a collaborative, interdisciplinary instructional model aimed at dramatically increasing student engagement; career-technical standards and work-based learning approaches with academic standards and a focus on the social-emotional well-being of students (Ball & Cohen, 1999;Darling-Hammond et al., 2017;Farnan et al., 2014;Garet et al., 2001;Schleicher, 2012).

Methods
This study applied a mixed-methods research design to examine teacher's knowledge of and confidence in designing a Project Based Learning curriculum. Data collection focused on inservice teachers who completed a 3-unit, 16-week course part of a Master's degree program in Curriculum & Instruction (C & I). For consistency, the terms participants or teachers are used interchangeably to refer to this group.

Participants
Participants included 16 in-service teachers who completed a course on Curriculum, Instruction, and Assessment as part of the M.A. program in Curriculum and Instruction. Participants for this analysis represented purposeful sampling based on successful completion of a curriculum design course in the M.A. program in Curriculum & Instruction program at a large comprehensive University in the Western region of the United States. This sampling strategy served to identify and select participants knowledgeable about and experienced with the phenomenon of interest (Creswell & Clark, 2011;M. Q. Patton, 2002). The 16 participants in the study were secondary school teachers from 5 different districts, representing a range of curricular areas, including English, Science, Social Studies, and Math. Table 1 describes teacher characteristics, including gender, years of teaching experience, and school type.

Course design
Teachers in this course met once a week for two hours and forty-five minutes for 16 weeks. The primary goal of the course was to enable teachers to craft an integrated curriculum aligned with industry-based technical knowledge and principles. Teachers designed the foundational aspects of a program of study that included a college preparatory curriculum, Career Technical Education course sequence, student learning outcomes, and an interdisciplinary PBL unit. Teachers worked in instructor-selected cross-disciplinary teams of 4-6 teachers.
The course was taught by a faculty member with expertise in curriculum design and PBL. In addition, assistance was provided by a graduate student with expertise in PBL and the use of instructional technology. The instructor modeled a PBL approach by engaging teachers in collaborative, inquiry-based activities that teachers could implement in their classrooms. Table 2 summarizes activities and assignments in the course. The primary focus of the first three weeks was to immerse students in a learner-centered/problem-based learning dynamic through which PBL could be modeled in the context of a career-themed academy.
Participants were guided through constructing a PBL unit and a cross-curricular unit integrated and organized around a central, career-themed issue or problem. The PBL procedures used in this study were based on the PBL Works 1 model, which includes the following elements: 1) Content knowledge and application of 21 st Century skills, 2) challenging open-ended projects or questions, 3) inquirybased, 4) authentic, 5) student-centered, 6) reflective, 7) time for revision, and 8) formal presentation. When implementing authentic project-based learning instruction, the gold standard includes all components of the PBL model in the learning environment (Buck Institute for Education [BIE], 2016).

Data collection
Data sources for this study included two pre-post surveys, one measuring knowledge of PBL principles and one measuring confidence related to PBL design, an end-of-course interview, and an integrated, cross-curricular PBL-unit completed during the course. To answer the knowledge component of research question 1, participants completed a 28-item pre-post assessment. The survey items asked about knowledge related to desigining, planning, and implementing PBL, including assessment, technology use and student personalization. Additional items asked about PBL practices and conditions such as school structure, demographics, background variables, and professional development opportunities. A ten-item survey was administered at the beginning and the end of the course to determine changes in teachers' confidence in designing and implementing PBL units. Participants were asked to rate their levels of confidence for performing PBL design tasks on an eleven-point scale, from 0 = "certain I cannot" to 10, "certain I can." The end-of-course interview asked participants to provide their thoughts about the course, what they learned, plans for implementing PBL, and perceived benefits and challenges in implementing PBL units within the context of teaching 21 st Century skills. Other questions focused on teachers' perceptions related to 1) the ability to plan and teach PBL units in the context of a career-themed academy; 2) factors that contribute to the design and use of PBL units in the context of secondary schools; and 4) the extent to which PBL could advance the expansion and sustainability of college and career readiness reforms.

Data analysis
Quantitative data were compiled and, where appropriate, data were statistically compared. Descriptive statistics and frequency distribution tests were conducted to identify means among the participants. I looked for evidence of changes in teachers' knowledge of PBL unit design, confidence related to the design of PBL units, and examined teachers' perceptions of the benefits and challenges of integrating PBL curriculum design.
All interview data were analyzed using qualitative methods. As M. Patton (2015) explains, "the evaluator using a qualitative approach seeks to capture what a program experience means to participants in their own words, through interviews, and in their day-to-day program settings, through observation" (p. 273). After an initial review of the data, the researcher developed preliminary deductive codes based on the literature and a cursory data review. Codes emerging from the data were reviewed and appropriate exemplar passages were identified for answering research questions. The use of three different data sources-surveys, knowledge assessment, and end-of-program interviews-allowed for triangulation of data, contributing to the study's credibility (M. Patton, 2015). Thick descriptions in participants' own words were used whenever possible In the discussion forum, teachers completed readings and reviewed videos that explored the student experience in a career-themed academy. Prompts: 1) What are some of the challenges to crosscurricular integration? 3) What structures/supports would you need to successfully plan and implement a project like those features in the videos?
In this assignment, teachers worked in design teams to establish a new career-themed academy. Activities included: (1) Determining the district's graduate profile.
(2) Determining a pathway theme that aligns with local community/industry needs and district/ school standards.
(3) Vision and mission statements that align with the goals and needs of the school, local industry community, and its students (4) A professional presentation that included the following: (a) Graduate Profile to contribute further to the credibility of the findings (Saldana, 2016;Yin, 2018). In reporting the findings, the names of participants have been changed to protect the identity of individuals.

Findings
Data from pre-course surveys point out the level of experience, and PBL training teachers received before the course. Teachers were asked to rate themselves in terms of the level of expertise with PBL, and 68% of the teachers rated themselves as beginners, while 31% said they considered themselves to be at the intermediate level. The survey also asked teachers whether or not they had received any level of instruction about PBL or similar inquiry-based instructional methods during their pre-service teacher education program. Results indicated that 50% of teachers had not received any PBL related instruction. While the other 50% indicated that they had received some basic information about teaching with PBL within the previous five years.
Data from the post-course interviews revealed diverse teacher experiences with PBL before taking the curriculum design course. Savannah, for example, shared that before the course, "[my level of understanding] was at a zero. I heard what it was, but I didn't understand what it was." Other teachers shared that before starting the course, they had heard of PBL, but, like Savannah, their understanding was limited. More than a third of teachers described that they had heard about PBL but had very little knowledge of its design principles and curricular elements. Jon shared: I was just aware of the name. But I really didn't have an understanding of what it actually entails to create a PBL unit. I was familiar with a lot of the concepts, although I didn't necessarily know the academic language for it.
Participants' pre and post-survey results showed an increase in teacher's knowledge and confidence in designing and implementing PBL units. While data from post-course interviews revealed that teachers perceived both benefits and challenges of designing and implementing PBL units in a classroom environment. In addition, teachers reflected on how well a PBL curricular approach could expand and sustain career-themed academies.

Changes in teachers' knowledge of PBL design
Participants in this study showed improvement in their knowledge of the principles of PBL design. The following table (see , Table 3 below) compares pre and post self-reported scores related to knowledge of PBL design principles and shows an overall increase in mean scores. The most significant increase is shown in teachers' knowledge of effective assessment tasks for PBL projects, followed by teachers' ability to create projects that cover the required curriculum. The two areas where teachers demonstrated a slight increase in their perceived knowledge of designing PBL units for the classroom had to do with organizing students into collaborative groups and providing the appropriate scaffolds for enhancing students' knowledge of content.
Data from the post-course interviews also suggest that the course improved their understanding of project-based learning and how to implement PBL units in their classroom. Participants described how their perspectives shifted as they enhanced their understanding of how PBL works. For example, during post-course interviews, several teachers shared that they initially believed PBL was simply an end-of-unit activity, where students have an opportunity to demonstrate what they learned. By the end of the course, they agreed that PBL is an excellent alternative to general textbook learning and allows teachers to work on many elements and standards that need to be addressed as part of the curriculum. One teacher reflected There are a wide variety of options for what project-based learning could look like. It doesn't have to be them creating something huge. I have a better understanding of what it should look like.
Other teachers described learning how to develop practical questions to accompany tasks. Liz, for example, reflected on her ability to design driving questions to launch her PBL unit, "I learned the importance of phrasing the driving question to make sure that it made sense in the real world, not just within my history curriculum. I also implemented a lot more opportunities for students to selfreflect throughout the entire PBL unit." Similarly, Michael commented that "having the right driving questions and allowing students to develop their own goals, their own direction with whatever project or question I can bring to them, allows me to maintain the standards and teaching what I'm supposed to teach." In reflecting on factors contributing to the design and use of PBL units, participants indicated that lectures, learning scenarios, and in-class simulations gave them a better understanding of Project-based Learning (PBL) principles and PBL methodologies and curricula. Participants also reported that working in peer groups and chunking tasks and activities into smaller parts, contributed to their knowledge and skills. Teachers implemented the theoretical information from the course into practical applications in their classrooms. This teacher's comments were representative of the experiences of most teachers in the study: I think the professor's guidance really was a big help. I thought the Project [assignment] was really useful 'cause it made me reflect on the PBL unit I'd already worked on. It really helped me refine it and make it more focused, and improve it.
Several teachers agreed, this course aligned PBL knowledge, application, and practice. Sammi's comments were typical of other participants in the study: I've really enjoyed the application aspect of it. It's been a lot of work, but it's been the type of work that you can see the effects right away. We're learning about how to frame a question, how to frame a PBL question, and then we're going back into the classroom and applying it.
Emily noted that she liked the fact that she was able to spend class time and ask the professor different questions It was helpful to have an expert to go to. Compared to my old school, when we were doing PBL, nobody was really an expert, and nobody had the answers. Nobody was able to guide me and give direction like the professor.
Data from teacher interviews indicate that the course provided information, time, and support to develop their knowledge and skills in designing PBL curriculum units. For example, Jenny reported that the PBL and interdisciplinary unit assignment "really helped me to see what I was doing, whether it was actually PBL or if it was just sort of a project that we were calling PBL." As Jenny's comments suggest, explicit instruction in PBL with a focus on strategies has been helpful in "seeing where we could kind of beef it up and make it more authentic and applicable for students, instead of just throwing the PBL label on something that wasn't." Laura commented that her experience and success with the PBL unit she designed and implemented encouraged her to expand her use of PBL beyond what she designed for the course. Ruth, a teacher with experience implementing PBL, confirmed that she was able to think through and refine key elements of her unit, including student self-reflection, student collaboration, and a website to access all the information students needed.
Teachers reported that the resources available in this class provided the proper support to understand and implement PBL in college and career pathways. Emma and several others expressed that the vastness of resources available was critical to their success in the course. Emily shared that she and others "were able to find good examples of PBL units to use in our own classrooms and as inspiration for my own units." Laura, for example, shared that having access to the Buck Institute's resources and the handbook was beneficial. She revealed that having the actual handbook served as a great reference tool. She shared that "I have it in my classroom. And I still use it for creating an essential question or a driving question, or something that's projectbased."

Changes in teachers' confidence related to PBL
Teachers recognized the advantages of the PBL design course and reported improvement in their confidence related to different aspects of PBL design. The confidence level was measured on a scale ranging from 0 = "certain I cannot" to 10 = "certain I can." For example, teachers were asked to rate their confidence related to their ability to design critical aspects of PBL units. Table 4 shows an overall increase in teachers' perceptions of their ability to implement PBL principles in the classroom. The most significant area of growth pertained to teaching selfregulation skills to students, with an increase of 1.81 points.
By the end of the course, 62% reported that they felt well prepared or very well prepared to use PBL to teach and assess student learning beyond academic content. Student learning of academic skills and content is key to a well-designed PBL unit. However, PBL also requires supporting students in their collaborative planning and refinement of projects. Monica, for example, reflected on the various elements involved in working in groups: "it's good to remember the group cultures and issues that come along with it and the egos and who's becoming the leader of the group, who's missing from the group, who's not contributing, making sure everyone is working together and understanding the goal and we're all on the same page and we're not working against each other." Moreover, working in groups served a reminder of what to expect when designing collaborative group projects in their own classroom: "that helps make me remember how to appoint group roles to people and think about where can groups make mistakes the most. When I see students do it, it's one thing, but when I see it happening with my group, it makes it easier to see it, to understand it." In areas related to the implementation of PBL, teachers also reported an overall increase in their ability and confidence level. Table 5 shows mean scores indicating the rate at which teachers felt they could implement specific PBL related strategies in the classroom context. Teachers increased their confidence in teaching students how to set goals, organize their work, and monitor themselves as they worked on PBL projects. In addition, teachers demonstrated an increase in their ability to manage and balance time spent on projects. Furthermore, teachers increased their ability to guide students through PBL related problems rather than simply give students the answer to the problem(s).
In post-course interviews, teachers shared that figuring out how to support students as they work through projects takes time. Sammi, for example, reflected on the PBL unit she designed "It's definitely working in a lot of the elements and standards that I need to be addressing. I think it's a good alternative to general textbook-style learning. But, I need to get better at giving them a chance to work together and apply their learning, before I jump in and give them the answer." The shift to a more authentic, inquiry-based and college-and-career ready curriculum requires teachers to develop a new skill set.
In addition, the majority of the participants (n = 15) indicated that they felt comfortable asking their students to work on multidisciplinary projects at least a few times per year. Laura, in particular, indicated that what she learned in the course encouraged her to do more projectbased learning units in her A.P. courses. She shared, "based on the success that I had with the small bit of PBL I was able to try out, it's really encouraged me to expand beyond the one thing that I tried this year."

Teaching 21 st century skills through PBL curriculum
Several teachers reported that infusing PBL into the curriculum helped them teach content knowledge and skills more effectively. More than 60% (n = 10) considered it especially important to use PBL to teach skills beyond academic content such as group work, presentation, project management, and 21 st Century skills. An overwhelming majority (n = 15) considered promoting students' civic engagement and contributions to the community and the world an important reason to use PBL. Teachers (n = 15) also affirmed that PBL made learning more personalized, and tailored to student's interests or needs. Teachers' perceptions of positive factors related to the implementation of PBL as an aspect of 21 st Century skills included designing a more fun and challenging curriculum (see , Table 6). Guide students to solve their problems rather than giving them the answers.
6.63 7.88 +1.25 Other positive factors included improved levels of engagement, increased relevance, and connection to the real world. More than half of the teachers conveyed that they valued PBL for its ability to engage students and show them connections between academic content and the real world. Laura shared her thoughts, "most important would be real-world application because that really helps students buy-in and then they're more willing to do higher-order work when they feel like there's a real-world or authentic purpose behind what they're doing." Other teachers emphasized how choice creates excitement and learning among students in class. Sara, for example, discussed: I give students more choice and voice in what they're doing and I release them to find their passions while also getting them to learn the content.
Three teachers described how PBL allows for the integration of skills and content. In a representative comment, Jeff explained, "the different skills that I can implement throughout a project-based learning unit are much more meaningful than teaching those in isolation." Chris reflected on the role that collaboration plays in the success of PBL units. She commented, It's really important to teach students how to collaborate when they're working on group projects. If I'm gonna grade them on collaboration, I need to teach them how to collaborate in the process.
Results from the post-course survey identified different challenges in implementing PBL in the classroom. The scale ranged from 1 = "not a challenge" to 3 = "a major challenge." The most frequent challenges teachers reported were student attendance issues and behavior problems (see , Table 7). For example, teachers identified classroom size, lack of time, and resources as moderate to major challenges in implementing PBL units. Moreover, more than half indicated that student attendance presented at least a moderate challenge. A lack of experience among students and the heavy reliance on direct instruction were also identified as challenges. Lack of time and lack of professional development were relatively infrequent challenges.
During interviews, teachers reiterated the challenges they faced with implementing PBL curriculum in their classrooms. In the post-course interviews, several teachers agreed with Jenny when she shared, "the most concerning thing, is at least at our school site, is chronic absenteeism among students. Over the course of a PBL unit, especially since we're on a block schedule, I only see them every other day for about 85 minutes a period. If they miss any day of that, it's a lot for them to try and make up because there's a big step that was missed. That's probably the most glaring concern that I have at this point." In addition, several teachers mentioned the lack of time available to plan, design, and implement PBL units.
Several teachers also recognized the importance of planning in the design and implementation of integrated PBL units. Jacob, considering the relevance of the planning, indicated, "planning is the most important because if you try to come up with a PBL unit without the right amount of planning and resources and getting help, it's very unlikely to be successful." Similarly, Noah shared that "when you are intentional with the planning, everything will go a lot smoother." In addition, participants considered teacher collaboration a critical aspect in the development of PBL related assignments, particularly the interdisciplinary unit design projects. For the most part, teachers enjoyed the collaborative nature of the course and seemed to connect what they were learning in the graduate course to their teaching contexts. While teachers consistently shared how much they enjoyed the opportunities to collaborate in class, they also reported that collaboration with colleagues in the context of their school sites could be challenging. Mike shared, "at work we're forced to work with different people." Mike further reflected, "you have to learn how to listen to other people's feedback and change your stuff and collaborate well." Liz also commented that adopting a more student-centered approach to the curriculum could be isolating, especially in an environment where no one else sees the value in adopting PBL strategies. Similarly, Erin shared her frustration with being in a school where many people were hesitant towards a PBL approach. She commented, "I feel like PBL has the best chance to do all the things I want my students to do, but there isn't full buy-in. Everybody is doing their own thing, and that's not enjoyable." Erin's sentiments reveal the complexities of implementing curricular reform with little or no buy-in from teacher colleagues.

Teachers' perceptions of PBL approach to curriculum
At the end of the course, participants were asked to list the three most important things they learned about implementing a PBL approach in their classrooms. Several participants expressed their belief that PBL provided the most effective instructional model for delivering a rigorous curriculum linked to 21 st Century skills and work-based learning opportunities. In interviews, participants consistently said that the course helped them better understand the connection between 21 st Century skills and PBL curriculum design in their classes. Ruth commented, "By taking PBL and putting it into your courses, you can broaden the content that you're teaching." Teachers came to value PBL as a powerful teaching method in which students learn college and career readiness skills and develop reading, writing and math skills as well as master course content. Jon shared, "sometimes we're trying to figure out how can we make learning relevant in our classroom, but really PBL is a vehicle for that." Similarly, Chris shared, "there [are] a lot of places for overlap in terms of characteristics of effective college and career readiness strategies, and the effective implementation of project-based learning. I think they work very well and synergize." Throughout post-course interviews, teachers affirmed their belief that PBL could be the approach to accomplish the goals of the college and career ready initiatives. Sammi recognized: The more I understand, the more I think about career readiness, the more I understand that PBL is kind of the way to go. I mean, the work-based learning opportunities, and incorporating academic and career -the easiest way to do that is pretty much, creating these projects that incorporate all these other courses and content areas and getting the professionals in the classroom. I think they go hand in hand.
Teachers consistently shared that applying PBL approach to curriculum could provide a framework for the authentic application of content and skills while opening up the curriculum to an industry theme that could bring relevance and real-world application to the classroom. Although teachers believed that PBL was an essential part of current efforts to reform the high school experience for all students, PBL could not fix the everyday challenges they faced, like poor attendance, disengagement, and lack of self-efficacy.

Discussion
The main purpose of this study was to examine current teachers' professional learning experiences in a graduate-level course focused on developing 21 st Century teaching skills. The candidates in the program consistently said that the course helped them better understand the connection between a project-based learning approach and 21 st Century skills development in their classes. Most teachers believed PBL was the most effective instructional model for delivering a rigorous curriculum linked to 21 st Century skills and work-based learning opportunities. The findings from this study revealed a strong positive relationship between teachers' knowledge of and confidence in designing integrated PBL units, with guidelines provided by faculty regarding these projects. These findings suggest that a sustained focus on pedagogy, curriculum, and skill acquisition is critical in developing 21st-century teaching skills. Focusing on classroom processes and teacher practices that support the development of 21st-century skills in the classroom can serve as an essential first step.
This study contributes to the body of research that indicates a meaningful change in the classroom involves sustained collaborative practices for teachers to develop implementation skills (Ball & Cohen, 1999;Darling-Hammond et al., 2017;Garet et al., 2001). The existing literature expresses a need for additional education and training for educators (teachers, counselors, administrators) to reform the high school experience. According to Darling-Hammond and McLaughlin (2011), teacher education that results in changes in pedagogy requires teachers to be active in the learning process, learn through the same methods they will be using with their students, and engage in collaborative inquiry and reflection. In other words, to "understand deeply, teachers must learn about, see, and experience successful learning-centered and learner-centered teaching practices" (Darling-Hammond & McLaughlin, 2011, p. 83).
The findings from this study suggest that sustaining and expanding the development of 21 st Century skills can be taught and enhanced through the integration of PBL curricula that foster the development of students who can think critically, pose and solve problems, and work collaboratively (Bell, 2010;Brears et al., 2008;Mioduser & Betzer, 2007;Saye & Brush, 2004;Wynn & Okie, 2017). The innovative uses of project based curriculum, and collaborative work, depend on substantial changes in how we prepare and support teachers once they enter the classroom. Research thus far indicates that teacher education and professional development need to be of sufficient quality and quantity to affect change in teaching practices (Fishman et al., 2003;Hemker et al., 2017;Tom, 1999). Moreover, teachers need time to think about, discuss, and practice methods to adopt those new to them (Garet et al., 2001).
The findings demonstrated that meaningful teacher learning, in the context of a graduate-level course, played an essential role in enhancing teacher's knowledge and understanding of interdisciplinary project-based curriculum and instruction. Moreover, evidence suggests that teachers could enhance their skills and knowledge about PBL design principles to integrate the curriculum across disciplines, resulting in student-led projects that prepare them for 21 st Century college and careers. Teachers valued learning opportunities that helped them unpack education reforms, in the context of their classrooms. Findings from this study suggest that aligning the educational program to reform-minded practices could impact teachers' knowledge. Designing Master's degree courses focusing on making teaching and learning more authentic, more relevant, more rigorous, and connected to the outside world could lead to exemplary instruction for high school students in urban school communities.
While this research served to confirm the small, but-growing body of literature on the connection between PBL curricula and 21 st Century skills development, it raised a few related questions that are worth exploring further. For example, how do a group of teachers work collaboratively to develop PBL units? Specifically, what knowledge could be gleaned by observing teachers during the development of a unit, its presentation in the class(es), student work on the project, and the final presentation of projects. Another question relates to how the choice of curriculum might impact the effectiveness of PBL strategies. Lastly, more research is necessary to develop frameworks on building teacher capacity in applying the principles of 21 st Century skills through an integrated, inquiry-based curriculum that is relevant and rigorous enough to prepare students for life beyond high school.
In the United States and around the world, education systems have invested in the capacity of teachers entering the profession. However, it is also important to focus on improving teacher's capacity to teach 21 st Century skills. Implementing improvements in curriculum and instruction have important implications for building the capacity of teachers, including those related to teacher learning, professional development, and the preparation of teachers. Given that there are more than 1.4 million secondary public-school teachers in the United States, preparing teachers to meet these demands is a massive undertaking (U.S. Dept of Education, 2019). Nonetheless, Colleges of Education, educator preparation programs, and advanced degree programs like the one featured in this study are developing the educational strategies and systems required for all children to achieve the knowledge and 21 st Century skills necessary to succeed.