Background: This study explored science teachers' participation in a professional development partnership with informal science institutions (ISIs) designed for urban middle school science teachers, known as the "Urban Advantage Science Initiative." The teacher training involved a whole school focused approach, providing teaching strategies, collaborative situated experiences, and specific classroom resources for implementing and guiding science explorations both at ISIs and in the formal classroom. The conceptual framework for the study incorporated a situated perspective model with situated, social, and distributed cognition. Urban Advantage Science Initiative Purpose: This long-term situated learning model engaged teachers in over 100 hours of training over five years, with an option to continue in select educational activities in subsequent years. Training was held at eight ISIs in New York City. The purpose of the study was to analyze impacts on teachers' pedagogical philosophies and practices. Sample: The ways teachers translated program principles into their practice was investigated through interviews with nine teachers and three administrators (N = 12) to provide broadened perspectives. The teacher sample was drawn from a larger group of 253 teachers with at least four years of experience in the program. Design/Methods: The data of this phenomenological qualitative study were examined and integrated with the a priori conceptual framework to create an emergent explanatory framework for changing pedagogical practice and teacher motivation through a schoolwide professional development partnership with ISIs. This framework included two major components: 1) improved teacher motivation, and 2) pedagogical change. Results: Teacher motivation was heightened because of their situated learning experiences at ISIs, the positive changes in their science pedagogy, and their involvement in a professional community of like-minded science educators. Conclusion: As a result of this whole-school focused program that included specific roles for teachers and administrators, the long term, sustained ISI-based professional development model improved teachers' and administrators' perceptions of science teaching practices.