This article considers the impact of a high-stakes testing and reporting requirement on students using publicly funded vouchers to attend private schools. We describe how such a policy was implemented during the course of a previously authorized multi-year evaluation of the Milwaukee Parental Choice Program, which provided us with data on voucher students before and after the reform, as well as on public school students who received no new policy treatment. Our results indicate substantial growth for voucher students in the first high-stakes testing year, particularly in mathematics, and for students with higher levels of earlier academic achievement. We discuss these results in the context of both the school choice and accountability literatures.