California, Florida, Illinois, New York, and Texas enroll close to 40 percent of the nation's public school students. The importance of these "Mega-States" goes beyond the sheer size of their population. They now serve more than half of the nation's English language learners (ELL), as well as some of the largest concentrations of children from lower-income families. As policymakers and educators look at the nation's changing demographics and explore ways to close achievement gaps, the educational progress of children in these states is of interest far beyond their state borders. That's why the National Center for Education Statistics and the National Assessment Governing Board focused this special report on educational outcomes in the five largest states. This report provides a more in-depth look into the performance of specific student groups and performance by subject, including: (1) recent assessments; (2) comparisons to the nation and among the five states; (3) highlights of gains for student groups, including those that performed higher than their peers in the nation; and (4) student performance at or above the NAEP "Proficient level." The results presented by each subject area are for public school students only. The National Assessment of Educational Progress (NAEP) reports results using widely accepted statistical standards; findings are reported based on a statistical significance level set at 0.05 with appropriate adjustments for multiple comparisons. Readers should note that writing results were not included in this report because the 2011 writing framework begins a new trend line. In addition, the 2011 computer-based writing assessment was not administered at the state level. Technical Notes are included. (Contains 19 figures, 7 tables, and 2 footnotes.)