A significant challenge for large-scale system-wide educational change is reconciling the importance of teacher ownership with the work of scaling up successful innovations. This article explores this dilemma in the context of a remarkable statewide transition to Activity Based Learning (ABL) in the government schools of Tamil Nadu, India. ABL, a pedagogical approach grounded in child-centered philosophies of learning, was developed by classroom teachers and educational leaders seeking to reach children disengaged from school. Advanced by reformers who respected teachers and understood the importance of teacher ownership in educational change efforts, ABL reached every primary-level government school in the state through a rapid scale-up. Drawing primarily on interviews with teachers, reform leaders, and other state-level officials, we explore the roles and forms of participation made available to teachers at different stages of the reform initiative. We also discuss how leaders built responsiveness to teacher feedback into each stage of scaling. We argue that the case of ABL in Tamil Nadu illustrates a powerful rethinking of system-level change, one that promotes teacher ownership through a movement-like approach in which leaders build egalitarian partnerships with classroom teachers and invite them into the educational change process, even through rapid and extensive scaling.