Recent research has examined the influential role coaches may play in supporting teachers' collective capacity building for instructional improvement. While emerging research is promising, much remains to be learned about collaborative approaches to coaching, particularly in schools with the greatest opportunity gaps. We draw on extensive longitudinal qualitative data to explore a collaborative approach to coaching in urban middle schools under pressure to improve math outcomes. Findings reveal key coaching strategies to promote teacher team capacity building, including fostering student-centered discussion and collaborative relationships, tailoring capacity-building opportunities to provide access for all teachers, and negotiating across teachers and leaders to support improvement efforts. This work was complicated by conflicting expectations between leaders and teachers as well as challenges with addressing teachers' misconceptions about math content in group settings. These findings reflect the need for ongoing capacity building that supports coaches as they attend to group dynamics and accountability pressures.