The No Child Left Behind Act (NCLBA) requires that states improve academic performance so that all students reach proficiency in reading and math by 2014 and that achievement gaps close among student groups. States set annual proficiency targets using an approach known as a status model, which calculates test scores 1 year at a time. Some states have interest in using growth models that measure changes in test scores over time to determine if schools are meeting proficiency targets. To determine the extent that growth models were consistent with NCLBA's goals, GAO assessed (1) the extent that states have used growth models to measure academic achievement, (2) the extent that growth models can measure progress in achieving key NCLBA goals, and (3) the challenges states may face in using growth models to meet adequate yearly progress (AYP) requirements and how the Department of Education (Education) is assisting the states. To obtain this information, we conducted a national survey and site visits to 4 states. While growth models are typically defined as tracking the same students over time, GAO used a definition that also included tracking schools and groups of students. In comments, Education said that this definition could be confusing. GAO used this definition of growth to reflect the variety of approaches states were taking.