The article synthesizes research findings from studies examining how principals and teachers contribute to shared instructional leadership and the relationship of shared instructional leadership to teacher and student learning. Principals and teachers contribute to the leadership equation in each school in different ways, according to school context and personnel, but an important finding is that the ways in which teachers and principals lead are in tension. It is this tension, however, that is characteristic of leadership in schools that make steady, incremental, and effective instructional improvement. Teachers learn more when teachers and principals find balance in the gradual movement between the status quo and intentional change. Two other factors enhance teacher learning: the shared belief that teachers can and must educate every student, and respectful and open relationships among colleagues. With these conditions, teachers learn to be better teachers and student achievement increases.