A critical state-level indicator of progress in public education is student achievement annual performance and change over time. The Council of Chief State School Officers (CCSSO) has been very active in tracking and reporting on student achievement results and using state assessment scores and other data to analyze achievement trends. A central goal of the No Child Left Behind (NCLB) Act was to close the gap in student achievement between students from different social and economic backgrounds. A principal objective of the federal funding mandated under NCLB, the design for program initiatives, and the accountability provisions of the federal law was to reduce the extent of disparity in performance of students from different demographic groups within schools as well as differences in the demonstrated performance of schools, districts, and states. The present report uses two different measures of student achievement—state student assessments and the National Assessment of Educational Progress (NAEP) —to determine the degree to which achievement gaps have been reduced in the period of implementation of NCLB in states.