In this article we seek to understand the impacts of a third party governance reform implemented by the nonprofit organization, Partners Advancing Values in Education (PAVE), on school-level performance in Milwaukee's maure school choice environment. Specifically, we compare the performance of PAVE and non-PAVE schools on Wisconsin state tests, and explore the relationship between school advancement on PAVE's internal indicators and performance. We show that generally positive findings for schools with longer exposure to PAVE programming exist independent of school size, history, religious affiliation, or reliance on voucher revenues. The article speaks to the potential of third party governance reforms to improve school performance in mature choice environments.