Governments face many constraints in attracting talented managers to the public sector, which often lacks high-powered incentives. In this paper, we study how a civil service reform in Chile changed the effectiveness of a vital group of public sector managers: school principals. First, we estimate principal effectiveness by using an extension of the canonical teacher value-added model. Then we evaluate the effect of the reform on principal effectiveness using a difference-in-differences approach. We find that public schools appointed more effective managers and improved their students’ outcomes after increasing the competitiveness and transparency of their selection process.