The Center on Education Policy (CEP) analyzed trends over four years in the number of schools and school districts that did not make adequate yearly progress (AYP) in raising student achievement under the No Child Left Behind Act (NCLB). Using data from the Consolidated State Performance Reports submitted to the U.S. Department of Education by all 50 states and the District of Columbia, CEP calculated the percentage of schools and districts in the nation and in each state that did not make AYP based on testing in school years 2005-06 through 2008-09. Three key findings emerged from the analysis: (1) One-third (33%) of the nation's schools did not make AYP in 2009. This marks an increase from 29% in 2006 but a decrease from 35% in 2008; (2) More than one-third (36%) of the nation's school districts did not make AYP in 2009, up from 29% in 2006; and (3) The percentages of schools and districts that did not make AYP often fluctuated from year to year within the same state and varied greatly across states. (Contains 2 figures, 2 tables and 5 footnotes.)