Test-based accountability provisions of the No Child Left Behind Act (NCLB) require states to set standards, measure student progress, and intervene when schools fail to meet the standards. Together, these standards, assessments, and consequences make up a standards-based accountability (SBA) system. The SBA portion of the NCLB affects every public school in the nation and has already had a noticeable impact on the actions of schools and districts. Two broad questions were addressed in this study: What strategies are used in implementing SBA at state, district, and school levels? Which of those strategies are associated with changes in classroom practice? This study gathered information on implementation across several levels, to understand how variations across schools and classrooms affect student learning-the strongest emphasis of this work. Using large-scale quantitative data collection and small-scale case studies to examine SBA implementation in California, Georgia, and Pennsylvania, this study focused on elementary and middle school science and mathematics to associate implementation factors with student outcomes. Overall, the performance of schools has been improving in all three states over the past three academic years. However, it is important to note that the three states approached accountability and teacher quality in different ways. The states also varied in the nature and breadth of their standards. These differences underscore the importance of considering state context when examining the effects of SBA on districts, schools, and students.