A teacher professional development program for in-service elementary school science teachers, the Rice Elementary Model Science Lab (REMSL), was developed for urban school districts serving predominately high-poverty, high-minority students. Teachers with diverse skills and science capacities came together in Professional Learning Communities, one full day each week throughout an academic year, to create a classroom culture for science instruction. Approximately 80 teachers each year received professional development in science content and pedagogy using the same inquiry-based constructivist methods that the teachers were expected to use in their classrooms. During this four-year study, scientists and educators worked with elementary teachers in a year-long model science lab environment to provide science content and science pedagogy. The effectiveness of the program was measured using a mix of quantitative and qualitative methods that allowed the researchers to triangulate the findings from quantitative measures, such as content test and surveys, with the emerging themes from the qualitative instruments, such as class observations and participant interviews. Results showed that, in all four years, teachers from the REMSL Treatment group have significantly increased their science content knowledge (p less than 0.05). During the last two years, their gains in science content knowledge, use of inquiry-based instruction and leadership skills were significantly higher than those of the Control group teachers' (p less than 0.01, p less than 0.001 and p less than 0.05, respectively). Three themes resonated in the interviews with participants: science content knowledge growth, constructivist pedagogy and leadership skills. (Contains 6 tables and 1 note.)