This report focuses on the NYC Computer Science for All (CS4All) initiative's efforts to build schools' capacity to expand access to CS across the district. Launched in 2015, CS4All aimed to provide a meaningful CS experience to every student at least once within each grade band (K-2, 3-5, 6-8, 9-12). As the initiative matured, it also began to support schools in fostering a strong CS culture--emphasizing leadership, equity, and awareness of the potential of CS instruction to promote student engagement and learning. As other K-12 districts nationwide aim to expand student participation in CS, lessons from the NYC CS4All initiative's capacity-building efforts can inform implementation strategies and professional learning (PL). This report investigates the progress that NYCPS schools made toward reaching the initiative's goals and sustaining participation in CS among their students. It builds on past work developing progress ratings to capture the extent to which schools were reaching all of their students with CS, as well as the extent to which participation was equitable for historically underrepresented groups. The report provides results from a school survey and interviews with school leaders and teachers, providing a deeper examination of facilitators and barriers to scaling up CS offerings and building an equitable, school-wide CS culture. Finally, the report examines the experiences of schools with different CS participation trajectories over time, to understand what enabled some schools to sustain high rates of participation and what prevented other schools from ever offering CS. [This study was also supported by the Google Computer Science Education Research program.]