Fueled by present-day globalization and influx of migration, the unprecedented global demand for English language necessitates the provision of high-quality education for English language learners across the world. This picture places English language teaching at the top of the educational agenda in both English-speaking and non-English-speaking countries. As a result of this critical prominence of the global English language teaching enterprise, the need for preparing all language teachers (teacher-learners coming from a range of ethnolinguistic, cultural, racial age, backgrounds with various past teaching, learning and educational experience) for diverse teaching settings in the U.S. and international contexts is more pivotal than ever. The current dissertation research sheds an important light on this need by adopting a TESOL teacher education department and its three MATESOL programs as a research context, and by providing a multifaceted exploration of how program components provide affordances and constraints in developing a knowledge base for ethnolinguistically diverse teacher-learners to work effectively with English language learners in diverse teaching contexts. The current research project is a holistic descriptive case study utilizing quantitative and qualitative analyses to explore the perceptions of (a) an ethnolinguistically diverse group of teacher-learners who were enrolled in, (b) an ethnolinguistically diverse alumni who graduated from, and (c) instructional faculty teaching in three MATESOL teacher education programs housed in a large, research-intensive university located in a bustling metropolitan area in the mid-Atlantic United States. The data collection sources included questionnaires, a series of semi-structured, in-depth interviews, classroom observations, and programmatic documents. The current study primarily draws upon sociocultural perspectives and more specifically utilizes Activity Theory as an analytical organizing framework to examine the complex interrelations among the participants, and to identify existing institutionalized tensions and contradictions among systemic components in the activity system under scrutiny. Activity Theory has proven to be a useful tool to capture the complexity of this teacher-learning context, and gain insights into the personal, pedagogical, and institutional affordances and constraints embedded in the activity system. Activity theoretical analysis of individual and programmatic efforts towards preparing teachers for diverse teaching settings in the U.S. and international contexts brought together three interrelated results that highlight an increased need for (1) diversification and dynamic re-orchestration of programmatic efforts, (2) reimagining distributed agency, and (3) developing practicum alternatives. The study concludes with the urgency of embracing the critical need, role and importance of English language teacher education, re-examining the current efforts in our quest to prepare all teachers for diverse teaching settings. The study closes by providing a series of recommendations for diversifying teacher education practices and developing a shared accountability in teacher preparation for diverse teaching settings and contexts. [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.]