Assistant principals play a critical role in the success of any school. As the role of assistant principals has shifted from disciplinarian and task manager to instructional leader, it is important for principals to provide shared leadership opportunities to their administrative team. This qualitative study investigated principal practices of developing the leadership capacity of their assistant principals in New York City Renewal Schools. Research has shown that due to role ambiguity and the underutilization of assistant principals, many are left feeling unprepared to support their staff with curriculum development and pedagogical practices. To address these issues, the researcher interviewed 13 administrators to gain their perspectives on the importance of leadership development. This study focused on three research questions: (1) To what extent has professional development been provided to assistant principals to close the achievement gap in Renewal Schools? (2) What actions, if any, have principals taken to develop the instructional leadership capacity for assistant principals in Renewal schools? (3) What supports do assistant principals provide to principals to close the achievement gap in Renewal Schools? This study revealed that professional development was crucial in providing assistant principals with the instructional skills needed to support staff. It was also found that assistant principals benefited from targeted professional development around specific goals to improve student achievement in Renewal School environments. Additionally, leadership coaching helped to ensure the alignment of the principal's vision of the school and served as a way for administrators to reflect on their overall practice. Finally, systems that promoted instructional coherence helped building administrators improve student outcomes. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]