This dissertation research project presents the results of a longitudinal study that investigates the knowledge, beliefs, and practices of 13 preservice secondary science teachers participating in a science teacher credentialing/Masters program designed to integrate issues of equity and diversity throughout coursework and seminars. Results are presented in the form of three papers: The first paper describes changes in preservice teacher knowledge about contextualization in science instruction, where contextualization is defined as facilitating authentic connections between science learning and relevant personal, social, cultural, ecological, and political contexts of students in diverse secondary classrooms; the second paper relates changes in the self-efficacy and content-specific beliefs about science, science teaching, diversity, and diversity in science instruction; and the final paper communicates the experiences and abilities of four "social justice advocates" learning to contextualize science instruction in underserved secondary placement classrooms. Results indicate that secondary student teachers developed more sophisticated understandings of how to contextualize science instruction with a focus on promoting community engagement and social/environmental activism in underserved classrooms and how to integrate science content and diversity instruction through student-centered inquiry activities. Although most of the science teacher candidates developed more positive beliefs about teaching science in underrepresented classrooms, many teacher candidates still attributed their minority students' underperformance and a (perceived) lack of interest in school to family and cultural values. The "social justice advocates" in this study were able to successfully contextualize science instruction to varying degrees in underserved placement classrooms, though the most significant limitations on their practice were the contextual factors of their student teaching placements--in particular, the extent to which their cooperating teachers gave them the autonomy and planning time to design and implement their own activities and lessons. While the "integrated approach" to diversity and equity in science teacher education was, overall, successful in helping preservice teachers' "move closer toward" developing the beliefs, knowledge, and practices necessary for effective instruction in underserved classrooms, suggestions are given for increasing the effectiveness of the "integrated approach," particularly in the context of a one-year credentialing program. [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.]