The most sweeping federal education law in decades, the No Child Left Behind (NCLB) Act, requires states to administer standardized exams and to punish schools that do not make Adequate Yearly Progress (AYP) for the fraction of students passing these exams. While the literature on school accountability is well-established, there exists no nationwide study of the strong short-term incentives created by NCLB for schools on the margin of failing AYP. We assemble the first comprehensive, national, school-level dataset concerning detailed performance measures used to calculate AYP, and demonstrate that idiosyncrasies in state policies create numerous cases where schools near the margin for satisfying their own state's AYP requirements would have almost certainly failed or almost certainly made AYP if they were located in other states. Using this variation as a means of identification, we examine the impact of NCLB on the behavior of school personnel and students' academic achievement in nationally representative samples. We find that accountability pressure from NCLB lowers teachers' perceptions of job security and causes untenured teachers in high-stakes grades to work longer hours than their peers. We also find that NCLB pressure has either neutral or positive effects on students' enjoyment of learning and their achievement gains on low-stakes exams in reading, math, and science.