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 Arizona'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 Arizona's system is compared with other states. Arizona has several unique characteristics which contribute to the large number of schools making AYP in the state: (1) Unlike most states, Arizona considers each grade separately when determining whether a subgroup meets the criteria for accountability; (2) Arizona's 99 percent confidence interval, providing schools with greater leniency than the 95 percent confidence interval used by most other states in the study; and (3) Arizona's proficiency standards are relatively easy in the early grades. Compared to the other 27 states examined, Arizona places at the high end of the distribution in terms of the number of schools making AYP. Additionally, some sample schools make AYP in Arizona that fail to make AYP in most other states, most likely because Arizona's proficiency standards are relatively easy compared to other states and its particular rules result in fewer accountable subgroups. The report concludes that although in some respects, Arizona'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 10 footnotes, 5 figures, and 6 tables.) [For "The Accountability Illusion", see ED504712. For individual state reports, see ED504680-ED504694, ED504700-ED504711 and ED504719.]