The Council of Chief State School Officers (CCSSO) is working to respond to increased interest in the use of growth models for school accountability. Growth models are based on tracking change in individual student achievement scores over multiple years. While growth models have been used for decades in academic research and program evaluation, a wide cross section of policymakers at local, state, and national levels are now using different types of growth models. A total of 12 states are utilizing growth models that provide estimates of whether student achievement will meet Adequate Yearly Progress (AYP) state proficiency targets within three years. These models were designed to meet the requirements of the No Child Left Behind (NCLB) Act. In addition, 13 states have developed and implemented growth models as required by state policy; these models use different formulas to measure growth for students and schools. Finally, five states are reporting on growth under both NCLB and state policies. This paper is an overview and description of current state activities with growth models. Policymakers and educational leaders are also seeking more information on basic differences between various types of growth models and the assessments, data, and reporting systems necessary to implement them. CCSSO has developed an annual report and webpage focused on state accountability systems, and this paper provides a current snapshot of differences and similarities in growth models used by state education agencies. The present paper is one of CCSSO's recent efforts to provide information on this topic. (Contains 2 tables.)