Much has been written in the last decade about the spotlight that the No Child Left Behind Act (NCLB) shines on schoolperformance. Proponents and opponents alike are quick to discuss the law’s rigid definitions of school performance— exemplified by the classification of schools as making Adequate Yearly Progress (AYP) or not making AYP based largely on annual tests in reading and mathematics, disaggregating school performance by student subgroups, and requiring that all schools reach 100% proficiency. Yet for all its rigidity, the law has offered schools little guidance on how to make use of the performance data that the new systems provide or how to design improvement efforts. As policymakers discuss ways to change NCLB or design new federal education policies targeted at improving academic achievement, we present new research findings that can help to inform those discussions. In this CPRE Policy Brief, we examine the extent to which the assumptions in the law manifest themselves in the actions that school leaders take. This brief asks and answers the question: How do school leaders—administrators and teachers— respond to the results of state assessment systems and the pressure of performance-based accountability? And do those responses seem to matter to achievement outcomes?