Principals have a substantial effect on the quality of learning in their schools. Likewise, districts have a substantial effect on the quality of their leaders. A growing number of large school districts are focusing on two objectives to strengthen school leadership: (1) building a pipeline of new principals who are ready to tackle the most underperforming schools, and (2) fully supporting those leaders, especially during their novice years. Building a strong pipeline of new principals entails adopting high-quality leadership standards, applying district pressure on training providers to improve the relevance of their programs, hiring the right people, and attracting strong leaders to struggling schools. Once they hire new principals, districts have a continuing responsibility to promote their growth and success. To this end, districts need to develop better ways to assess principals, invest in mentoring and continuing professional development, provide good data and the training on their use, help principals and their teams focus more time on instruction, and plan for orderly leadership succession. The big lesson is that principals matter to the academic success of students and that district should therefore take a strong hand in selecting and training their leaders and cultivating their continuous success.