The Instructional Leadership Corps (ILC) is an innovative professional learning network in California in which teacher leaders collaborate and support their colleagues in developing teaching strategies and practices aligned with new content standards. Over more than 4 years, 100,000 teachers have been served by the ILC, through conferences and trainings, with overwhelmingly positive responses. The ILC changes the paradigm for teacher learning from one dependent on outside consultants to one that engages local professionals to lead ongoing learning within their own districts—and, in many cases, in other schools and districts in their regions. 
 
This new brief describes how the ILC has changed the professional development landscape in four regions of California, offering lessons about how teacher-led learning can motivate shifts in practice, enhance teachers’ professionalism and efficacy, and create supportive systems and strategic relationships that can sustain change.