This qualitative study investigates the development of science teacher leaders during and after professional development. It examines the impactful experiences during a teacher leadership program that allowed them to explore their leadership identity and how this identity manifests in their schools' post-program. The participants are 14 chemistry and physics teacher leaders from schools in the Southeastern U.S. who attended a five-year Noyce teacher leadership program. They are emergent leaders who entered the program with limited leadership exposure or expertise. Social learning theory provides the lens to examine during and post-program interviews with science teacher leaders. Three themes emerge from the interviews: 1) Redefining leadership, 2) Responsibility for others, and 3) Collaborative community that developed the science teacher leadership identity during and after the program. The findings from this study have theoretical and practical implications for teacher leaders, schools, and leadership development programs.