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 Wyoming'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 Wyoming's system is compared with other states. Wyoming's proficiency standards are relatively difficult compared to other states, and Wyoming's minimum subgroup size is smaller than most other states, meaning that schools in Wyoming have more accountable subgroups than do similar schools in other states. More subgroups in Wyoming elementary schools failed to meet their reading targets than their math targets, likely because proficiency standards in grades 3-6 reading are higher than those in math. Compared to the other 27 states examined, Wyoming places in the lower end of the state distribution in terms of the number of schools making AYP. The report concludes that although in some respects, Wyoming'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, 6 figures, and 5 tables.) [For "The Accountability Illusion," see ED504712. For individual state reports, see ED504680-ED504694, ED504700, and ED504719.]