This brief examines the New York City Public Schools' (NYCPS) Computer Science for All (CS4All) initiative's efforts to build teacher capacity and support the implementation of computer science (CS) education across K-12 classrooms. The initiative, launched in 2015, aimed to deliver high-quality CS education to all students by providing robust professional learning (PL) opportunities for teachers, including many with little or no prior CS background. As NYC's CS4All work evolves and CS education initiatives expand nationwide, the lessons highlighted in this report can inform planning and decision-making.