The Center on Education Policy, an independent nonprofit organization, collected and analyzed data from state Web sites and other sources to determine how many schools in the nation and in each state did not make adequate yearly progress (AYP) under the No Child Left Behind Act (NCLB). Findings of the study include: (1) About one-third of U.S. public schools did not make AYP in school year 2008-09; (2) In nine states and the District of Columbia, at least half the public schools did not make AYP in 2008-09. In a majority of the states (35 including D.C.), at least one-fourth of the schools did not make AYP; and (3) The percentage of public schools not making AYP varied greatly by state, from 6% in Wisconsin to 77% in Florida. These differences among states do not necessarily reflect the quality of the schools; rather, they are likely due to state variations in standards, tests, cut scores for proficient performance on those tests, and methods for calculating AYP. (Contains 4 footnotes and 1 table.)