The integration of student-centered learning (SCL) practices in higher education, particularly in Science, Technology, Engineering, and Mathematics (STEM) fields, is essential for addressing persistent challenges such as high failure rates among underrepresented groups. Institutions of Higher Education are increasingly emphasizing evidence-based, student-centered instruction, leading to the development of PD programs aimed at promoting instructors' adoption and integration of SCL practices, particularly in STEM. However, faculty resistance remains a challenge. Traditional PD approaches often focus on short-term outcomes without considering long-term instructor persistence or the contextual complexities of SCL integration. This dissertation research addresses these gaps by examining STEM instructors' role identities before, during, and after participating in SCL PD programs, using the Dynamic Systems Model of Role Identity (DSMRI) (Kaplan and Garner, 2017) to analyze development in identity formation. The study highlights the diverse ways participants integrate SCL into their role identities and the complex interplay between role identities, situational and contextual pressures, and instructional practices. The findings highlighted two emergent theoretical dimensions that characterized the different STEM instructors' incorporation of SCL into their role identities: Scope of Identity and Degree of Identity Integration. Differences in Scope of Identity and Degree of Identity Integration framed the different long term implementations of SCL by the different participants and provided an initial theoretical framework to conceptualize and evaluate long-term instructor change processes post-PD. A thematic analysis also highlighted how contextual/situational factors framed participant negotiation of departmental and institutional pressures and included institutional policies and procedures, coordinated courses and student achievement gaps. Emergent role identity elements of self-perceived fallibility and sense of community building were central to the successful identity negotiation of situational pressures around implementing SCL. Implications for theory, PD practice, and university policy are discussed, emphasizing the need for continued support, collaboration, PD design that promotes identity exploration, and understanding of the systemic influences shaping SCL integration in STEM. Future research should further explore the role of institutional and departmental culture in SCL integration, leveraging frameworks like the DSMRI to deepen our understanding of identity formation and SCL integration among instructors across disciplines and institutions. Additionally, collaborative efforts between university administration, course structuring, and instructional goals are essential to aligning institutional priorities with SCL implementation strategies, ensuring better student engagement, increased student success, and enhanced retention particularly for underrepresented students in STEM. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]