This qualitative, design-based research study explored the design, implementation, and outcomes of a professional development for mid-career K-8 science and engineering teachers. The Responsive and Empowering Science and Engineering Teacher (RESET) professional development was designed to support teachers in developing role identities as culturally responsive teachers, change agents disrupting inequitable educational practices, and advocates of students’ equitable access to and participation in science and engineering disciplines. Four mid-career K-8 teachers participated in RESET, which was embedded in a five-week summer program focused on solar energy engineering. The teachers engaged in activities designed to increase their knowledge of and pedagogical strategies for culturally responsive teaching. After each key event, teachers reflected on their experiences in terms of their role identities, including their purposes and goals, self-perceptions, beliefs, and perceived action possibilities for that role. Teachers also engaged in critical discussions examining how the strategies and practices might contribute to more equitable science and engineering practices. An embedded case study design was used, with RESET as the focal case and the four teachers as embedded cases, to examine teachers’ experiences during RESET and actions during the school year. I analyzed teacher surveys, semi-structured interviews, written reflections, audio recordings of the critical discussions, and researcher memos from during RESET and school year observations to determine the influence of RESET on teachers’ role identity development and actions. I also analyzed a series of conjecture maps created to detail the design and adaptations of RESET to explore the extent to which RESET’s targeted enactment processes and outcomes had been achieved and design and process conjectures had been supported. Findings varied across participants, with all four participants at least somewhat achieving the targeted outcomes, indicating that all of the teachers’ role identities were influenced by RESET. Three of four teachers translated their learning into actions as culturally responsive science and engineering teachers during the school year. In terms of RESET’s design, several of the conjectures were supported or partially supported. Implications for the second iteration of RESET and for the general scholarship on professional development for mid-career K-8 science and engineering teachers are discussed.