An evaluation of the Science Resource Leaders Program, which was funded by the National Science Foundation and administered jointly by the School District of Philadelphia and PATHS/PRISM. SRL sought to train a two-person team of teacher leaders at every Philadelphia middle school to plan and coordinate science programs and provide staff development. This report describes various types of SRL classrooms, examines how SRL participants acted as leaders in their schools, and assesses how SRL functioned as a teacher network. Research data shows that while the project increased positive teacher attitudes towards science and changed classroom practices, progress was limited by a shortage of resources. The authors offer recommendations for improving the program by deepening changes in classroom practice, strengthening science education across each school, and sustaining the teacher network created by SRL.