This chapter explores the relationship between accountability and school leadership. The argument is as follows: accountability systems work to the degree that they engage the knowledge, skill, and commitment of people who work in schools. The success of accountability policy depends on the development of what the author calls the practice of improvement – explicit strategies for developing and deploying knowledge and skill in schools. Accountability tends to lead to an underinvestment in knowledge and skill, and an overinvestment in testing and regulatory control. Correcting this distortion requires changing the relationship between policy and practice, particularly around the definition and development of leadership. The author develops a model of school leadership practice consistent with his proposed theory of accountability. He reviews ways in which policies might be used to increase leadership capacity for school improvement. Accountability policy will not increase school performance unless there is substantial investment in developing human capital focused on school improvement.