This protocol guides the review of research that informs the What Works Clearinghouse (WWC) intervention reports in the School Leadership subtopic area. The protocol is used in conjunction with the "WWC Procedures Handbook (version 4.0)" and the "WWC Standards Handbook (version 4.0)." Research has shown that school leaders can substantially influence student outcomes, including student achievement, and that some school leaders improve student outcomes at a much faster rate than others. The strong influence of school leaders on student outcomes as well as the variation in school leader effectiveness has led to the creation of multiple programs designed to help school leaders improve student outcomes. This review focuses on interventions aimed at making school leaders, specifically principals, assistant principals or deans of students, more effective at improving the achievement of students in grades PK-12. These interventions are targeted at adults who are considering becoming school leaders; undergoing preparation for school leadership; or already employed as school leaders. The interventions may be delivered in a variety of educational and training settings. Although the interventions are delivered to school leaders (or potential school leaders), this review focuses on outcomes for students, teachers, and school leaders. Student outcomes include measures of achievement, progression in school, social-emotional learning, and behavior. Teacher and school leader outcomes include those that research has shown are related to student achievement, including teacher instructional practice, retention of teachers and school leaders, and leadership practice.