In this paper, we examined data collected as part of a 5-year project designed to foster reform-based urban science teaching through teachers' communities of inquiry. Drawing upon a distributed leadership framework, we analyzed teacher "talk" during professional learning community (PLC) meetings. This analysis yielded five elements: teacher learning and collaboration, community formation, confidence in knowledge of content and guided inquiry, concerns about the impact of accountability measures on teaching and learning, and sustainability of reform. Follow-up interviews with participants reinforced the importance of these elements. While accountability measures were found to have a significant impact on science teaching, participants were also able to use their PLC-based experiences to develop strategies to deal with such external constraints. Facilitation and leadership also play key roles in establishing and maintaining PLCs in this urban setting. Finally, we present a revised framework that incorporates the elements we identified to describe those local and systemic factors critical for successful implementation and influence of professional development efforts. (Contains 1 figure and 4 tables.)