School leadership remains underutilized and underresearched. We set out to document the existing evidence base and lay out a research agenda for the future. This paper summarizes what the authors have learned from the existing research. This report has reviewed more than 70 studies, focusing on the empirical literature from the Global South. The purpose of this report is to summarize the evidence on what is known about: (1) The relationship between school leadership and student outcomes; (2) the status of school leaders in education systems; (3) the availability and impact of training programs that aim to improve school leadership skills and student outcomes; and (4) other enabling conditions, such as policies related to the selection, accountability, and autonomy of school leaders, that impact the quality of school leadership and effectiveness of school leadership training.