Teachers are professional learners and leaders. They seek to understand how their students learn, and they participate in programs that provide new instructional skills, curricular materials, and ways to become involved in their community. This study follows a science teacher leadership program over a three-year period of time. There were approximately 30 participants per year. The teachers who participated in the program came from two different states in the United States. Interviews, documents and surveys were used to follow the development of the program and the professional growth of the participants. The qualitative and quantitative analysis reveals that: not all participants became teacher leaders, there were different levels of difficulty associated with the presented leadership skills and knowledge bases, there are some essential knowledge bases associated with teacher leadership, the follow-up program varied between sites, and teachers engaged in leadership in different ways. For those in science teacher education, this study helps fill the void of research in this area, and it suggests that science teacher leadership should be an option for professional development.