A recent literature provides new evidence that school resources are important for student outcomes. In this paper, we show that school finance reform-induced increases in student performance are driven by those states that had test-based accountability policies in place at the time. By incentivizing school improvement, accountability systems (such as the federal No Child Left Behind act) may raise the efficiency with which additional school funding gets spent. Our empirical approach leverages the timing of school finance reforms to compare funding impacts on student test scores between states that had accountability in place at the time of the reform with states that did not. The results indicate that finance reforms are three times more productive in low-income school districts when also accompanied by test-based accountability. These findings shed new light on the role of accountability incentives in education production and the mechanisms supporting the effectiveness of school resources.