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 California'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 California's system is compared with other states. More schools in the study make AYP in California than in most other states. Although California has relatively high proficiency standards in reading and math, the percentage of students required to meet those standards in 2008 is relatively low. The minimum subgroup size for reporting purposes is relatively high, larger than that used by most other states examined in the study; therefore, the achievement scores of many minority, limited English proficient (LEP), and disabled students that are not counted separately for accountability purposes in California would be counted separately in other states. Compared to the other 27 states examined, California places at the high end of the distribution in terms of the number of schools making AYP. The report concludes that although in some respects, California'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 6 tables.) [For "The Accountability Illusion," see ED504712. For individual state reports, see ED504680-ED504694, ED504700-ED504711 and ED504719.]