As an intermediary between U.S. state and federal policy and the school, the school district, many scholars maintain, remains a key player in meeting the needs of school-level leadership. Moreover, the job of the principal is difficult and has become increasingly complex as a result of increased pressure, accountability, and oversight under the No Child Left Behind Act (now the Every Student Succeeds Act) in the United States. These two propositions raise important questions about what we know (and do not yet know) about how to support school leaders' learning and development in their quest to effectively lead a school. In this review, we use extant social-cognitive theories of motivation to organize the research on district effectiveness in pursuit of the following question: How does the district as a key player in school/instructional improvement facilitate conditions under which school principals' learning, development, and success are enhanced? In pursuing this question, we hoped to strengthen two particular weaknesses in this strand of scholarship: (1) the concern that research in this particular area is relatively atheoretical and (2) concerns about the applicability of this research to practice.