For many years now, researchers and school improvement advocates have largely focused on improving the quality of teachers as the main lever for increasing the quality of schools. Since students spend the most time with their teachers, these efforts made sense. However, recent research from the Wallace Foundation has found that the impact of principals on improving schools has been understated. Since principals are the people that recruit, develop, and support all of the teachers in a school building as well as other important tasks like building a supportive school climate, there is a strong case for increasing the effectiveness of our principals in order to improve the quality of our schools.