In 2014, The Wallace Foundation launched the Principal Supervisor Initiative (PSI), a four-year, $24 million-dollar effort to redefine principal supervision in six urban school districts. The initiative sought to help districts transform a position traditionally focused on administration, operations, and compliance to one dedicated to developing and supporting principals to improve instruction in schools. The initiative was motivated by an effort to increase student learning and achievement by improving principal effectiveness. Research has shown that strong principals are integral to strong schools and to raising the quality of teaching. Numerous studies have pointed to the importance of effective leaders for teacher satisfaction, teacher retention, school climate, parent engagement, and student achievement. Principal supervisors are a potential point of leverage for supporting and developing principals, but relatively few districts have invested in such efforts. The motivating hypothesis of the PSI is that changing the role of principal supervisors from overseeing administration and operations to providing instructional leadership can drive improvement in principal effectiveness. The report presents analyses of data from semistructured interviews with central office personnel, principal supervisors, and principals, as well as data from surveys of supervisors and principals in each of the six PSI districts throughout the United States.