This study from the Learning Policy Institute explored how California's Instructional Leadership Corps (ILC) gained traction and began to transform professional learning opportunities in their communities and regions. These efforts often addressed long-standing problems of practice and inequities in children’s access to high-quality instruction. Given that practitioner-led professional learning has often failed to gain a toehold in districts in which teacher leaders are appointed but not integrated into the work of the schools, the study examined factors that enabled the work of the ILC to grow and become rooted in various communities. The study examined the strategies used by ILC leaders both in conducting professional development and in connecting their work to the broader efforts of their districts and counties, and it also examined the perceived impacts on practice for teacher participants.