Latin American teachers' unions have stepped into the policymaking sphere and shaped education policies unrelated to regular workplace priorities like salaries and class sizes at notable moments. The literature on teachers' unions in Latin America has not addressed this, tending to focus instead on those unions' history and role in social movements, or their struggles against controversial education reform. This article links existing literatures in an effort to explain why teachers' unions sometimes break from their normal workplace demands to take an active role in education policymaking. Drawing on case studies of Brazil, Bolivia, Chile, Venezuela, and Guatemala, it argues that teachers' unions break out of this usual role and promulgate system-enhancing education policy in the context of society-wide social movements, such as those that lead to democratization or indigenous rights. However, only where these policies meet a receptive government are they translated from proposal to practice.