While numerous recent authors have studied the effects of school accountability systems on student test performance and school "gaming" of accountability incentives, there has been little attention paid to substantive changes in instructional policies and practices resulting from school accountability. The lack of research is primarily due to the unavailability of appropriate data to carry out such an analysis. This paper brings to bear new evidence from a remarkable five-year survey conducted of a census of public schools in Florida, coupled with detailed administrative data on student performance. We show that schools facing accountability pressure changed their instructional practices in meaningful ways. In addition, we present medium-run evidence of the effects of school accountability on student test scores, and find that a significant portion of these test score gains can likely be attributed to the changes in school policies and practices that we uncover in our surveys.