The intent of the No Child Left Behind (NCLB) Act of 2001 is to hold schools accountable for ensuring that all their students achieve mastery in reading and math, with a particular focus on groups that have traditionally been left behind. Under NCLB, states submit accountability plans to the U.S. Department of Education detailing the rules and policies to be used in tracking the adequate yearly progress (AYP) of schools toward these goals. This report examines Massachusetts's NCLB accountability system, particularly how its various rules, criteria and practices result in schools either making AYP, or not making AYP. It also gauges how tough Massachusetts's system is compared with other states. Massachusetts math proficiency standards range from a high of the 77th percentile in grade 4 to the 68th percentile in grades 6 and 8: to be considered proficient, grade 4 students must perform better than 77% of all other students in the nation. Although the reading standard is somewhat lower, ranging from the 65th percentile in grade 4 to the 30th percentile in grade 8, Massachusetts still expects approximately 95 percent of its grade 3-8 students to reach the reading standard in 2008. These dynamics, combined with the fact that Massachusetts does not apply a confidence interval to proficiency rate calculations, contribute to only one Massachusetts school making AYP in the study. Compared to the other 27 states examined, Massachusetts places at the very low end of the distribution in terms of the number of schools making AYP. The report concludes that although in some respects, Massachusetts's NCLB accountability system is working as intended by the legislation, NCLB shortcomings are also evident, and should be considerations for Congress in future reauthorizations of the act. (Contains 7 footnotes, 4 figures, and 6 tables.) [For "The Accountability Illusion," see ED504712. For individual state reports, see ED504680-ED504694, ED504700-ED504711 and ED504719.]