School districts throughout the United States are increasingly providing greater autonomy to local public (non-charter) school principals. In 2005-06, Chicago Public Schools initiated the Autonomous Management and Performance Schools program, granting academic, programmatic, and operational freedoms to select principals. This paper provides evidence on how school leaders used their new autonomy and its impact on school performance. Findings suggest that principals were more likely to exercise autonomy over the school budget and curricular/instructional strategies than over professional development and the school's calendar/schedule. Utilizing regression discontinuity methods, I find that receipt of greater autonomy had no statistically significant impact on a school's average math or reading achievement after two years of autonomy. I do find evidence that autonomy positively affected reading proficiency rates at the end of the second year of autonomy. These findings are particularly relevant for policy makers considering the provision of greater school-based autonomy in their local school districts.