The current mixed method study examined a Teacher Leadership Program (TLP) to determine to what extent participating teachers had changes in content knowledge (CK), practices, leadership skills, and leadership knowledge. The purpose was to determine if this program could be utilized to suggest a sustainable model for improving science education by utilizing teacher leaders to influence changes in their classrooms and at the school level. Participants included 65 K-8 participating teachers and 70 K-8 comparison teachers. Surveys, CK assessments, lessons, observations, and artifacts were analyzed using a-priori coding and descriptive statistics. Participating teachers had statistically significant gains over comparison groups in CK, practices, and teacher leadership skills and knowledge. The findings from this study contribute to the understanding of professional development (PD) for teacher leadership and the under-examined field of teacher leadership literature.