The purpose of this present ethnographic case study is to explore the initial and developing beliefs, understandings, and experiences of prospective language teachers as they engage in the process of learning about cooperative learning (CL) and in putting it into practice in a TESOL graduate program in the U.S. Data collection includes multiple interviews with seven purposefully selected graduate students (one focal student--the telling case; six sub-focal students) from diverse cultures, such China (1), Japan (2), Korea (1), Jordan (1), Poland (1), and the U.S. (1) and one instructor from a graduate TESOL methods course; artifact collection; and weekly observations of the course (16 students in total) during the fall semester of 2007. Based on the data collected and analyzed, the findings show the complexity of prospective teachers' beliefs, attitudes and actions and how the social nature of human learning connected with their thought process in the given context. One of the main findings is that the focal student's beliefs progressively changed from "learning individually" not favoring group work to a favorable one of "learning together" during one semester and her newly established belief was in action in her microteaching performance at the end of the semester. She and the sub-focal students also came to believe that the use of CL in their future teaching would be beneficial. Facilitation of their belief change seemed to be due to factors and experiences during their learning process in the TESOL methods course. For example, prospective "international" teachers' self-consciousness about their own English proficiency, and their cultural and societal dispositions created power struggles in their group, influencing their group works' interaction dynamics. The dilemmas that prospective teachers had in their group work became steppingstones, by advancing their critical thinking ability to reflect on their performances. This "reflection time" led them to generate and test their hypothesis, which contributed to their development of understandings and beliefs about CL and group work. It is also found that the instructor's "group structuring" and "class structuring" techniques, such as an integration of the strategy use of loop input, experiential learning and CL, were a powerful medium to influence prospective teachers' understandings and beliefs about teaching and learning. This maximized their learning potentials in a cooperative learning community that was built in their classroom, creating group zone of proximal development and attaining a level that they might not have achieved alone. Furthermore, prospective teachers' mental comparisons between their unstructured group work experiences in their other academic courses and their well-designed and structured cooperative group work in the TESOL methods course played a crucial role in forming their new belief about CL and constructing knowledge for developing well-designed and structured group work. The prospective teachers not only gained content knowledge in their courses but also gained knowledge on how to teach (pedagogical and practical knowledge) as they attended the courses by observing how their instructors organized and delivered the classes. Based on the findings of this study, a model of developing belief system was generated by modifying Ajzen's theoretical model (i.e., theory of planned behavior, 2005) to fit into a teacher education program. This may help to understand one's thought process while developing beliefs in relation to his or her action. This model is a useful reference for teacher educators and scholars, as it shows where an intervention might need to be integrated in order to change or improve a teacher's classroom actions (i.e., teaching performance). The findings may also offer new avenues for foreign language educators to maximize their students' learning experiences using CL instruction in a language classroom and/or a language teacher-training program. More educational implications and instructional suggestions are also discussed in this study. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]