Background: New York City is one of the most segregated school districts in the country, but between 2012 and 2021, school integration moved from a marginal to a central education policy. Existing narratives have emphasized the efforts of parents and school and political leaders, with less attention given to the significance of citywide coalitions of activists, especially youth activists. Purpose: We examine how grassroots activists contributed to advancing school integration policy, and the opportunities and challenges that resulted, through urban regime theory, and specifically "civic capacity," which highlights how various constituencies build a shared agenda for policy change. Research Design: Working in partnership with four youth interviewers at two integration activist organizations, we conducted 72 semi-structured interviews with New York City student, parent, and community activists. We also observed 36 hours of public meeting observations and collected publicly available documents, including 360 newspaper articles and policy documents, to triangulate our findings. Conclusions: We found that activist coalitions made progress in developing civic capacity through increased collaboration among diverse stakeholders, notably youth, toward a shared definition of integration. However, growing tensions with rival coalitions and the fragmented political landscape of NYC limited the strength and durability of civic capacity.