This book uses PISA data to show that a substantial proportion of students in OECD countries now attend schools that have high degrees of autonomy in different areas of decision making. But effective school autonomy depends on effective leaders, including system leaders, principals, teacher leaders, senior teachers, and head teachers, as well as strong support systems. That, in turn, requires well-distributed leadership, new types of training and development for school leaders, and appropriate support and incentives.