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 Washington'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 Washington's system is compared with other states. Washington has a relatively small subgroup size for its minority and low-income students, meaning that schools in Washington may have more accountable minority and low-income subgroups than similar schools in other states. Washington also has above-average proficiency standards, especially at the middle school level, and relatively high annual targets. Although Washington's 99 percent confidence interval provides schools with greater leniency than the more commonly used 95 percent confidence interval, the former factors make Washington among the most restrictive states in terms of the number of schools making AYP. Compared to the other 27 states examined, Washington places at the low end of the distribution in terms of the number of schools making AYP. The report concludes that although in some respects, Washington'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 9 footnotes, 6 figures, and 6 tables.) [For "The Accountability Illusion," see ED504712. For individual state reports, see ED504680-ED504694, ED504700-ED504711 and ED504719.]