This article presents findings from a multi-year, qualitative study of K-12 science teacher fellows involved in a grant-funded professional development program. This research hones in on Year 2 where we examine the actions our fellows have taken in their districts as science teacher leaders and their sense of agency. The following main themes emerged in the data: how science teacher leaders see personal/organizational change as a process; the importance of differentiated mentoring and support; the fellows' acceptance of roadblocks as part of the growth process; and finally, the value of reflection as a means to sustain leadership efforts beyond the fellowship. We explore the implications for professional development programs in districts, and in particular, those that address the need to cultivate teacher leadership.