Given the prominence of both instructional leadership and teacher leadership in the realms of school reform and policy, not surprisingly, both have also been the focus of extensive empirical research. But there have been limits to this research. It is, for example, unclear which of the many key elements of instructional leadership are more, or less, likely to be adopted in schools across the nation. Similarly, it is unclear which of these elements are more, or less, beneficial for school performance and for student learning and growth. Likewise, though the extent of teacher involvement in school decision making has been widely studied, there has been almost no solid empirical research on whether teacher leadership is beneficial for student learning and growth. These topics are the subject of a study the authors undertook, which this article summarizes.