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 have leeway to: (1) Craft their own academic standards, select their own tests, and define proficiency in reading and math; (2) Establish their own annual targets for moving students to the proficient level by 2014; (3) Apply confidence intervals to school proficiency rates; and (4) Determine when the size of a student subgroup within a school is large enough that it must meet AYP targets. This study examines NCLB accountability systems and basic AYP rules for 28 states as they operate in practice: Arizona, California, Colorado, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Kansas, Maine, Massachusetts, Michigan, Minnesota, Montana, Nevada, New Hampshire, New Jersey, New Mexico, North Dakota, Ohio, Rhode Island, South Carolina, Texas, Vermont, Washington, Wisconsin, and Wyoming. Overall report findings include: (1) Within the elementary school sample, the number of schools that made AYP varied greatly by state: almost all sampled schools failed to make AYP in some states, and nearly all of these same schools made AYP in others; (2) More consistency across states with the middle school sample (few of these schools made AYP in any state); and (3) When it comes to whether the performance of a subgroup will hurt a school's chances of making AYP, the state decision relative to minimum subgroup size is highly significant. The report concludes that overall evidence from the sample indicates that NCLB, as currently implemented, is not a discriminating system, but that accountability is not coherent. The authors suggest a more consistent accountability system is needed to improve schools in all states. The foreword for this report was written by Chester E. Finn, Jr., Michael J. Petrilli, and Amber M. Winkler. Three appendixes are included: (1) Methodology; (2) Estimated State Test Proficiency Cut Scores in Reading using Measures of Academic Progress; and (3) Estimated State Test Proficiency Cut Scores in Math using Measures of Academic Progress. (Contains 8 footnotes, 23 figures and 21 tables.) [This report was published in partnership with Northwest Evaluation Association (NWEA). For individual state reports, see ED504680-ED504694, ED504700-ED504711 and ED504719.]