The results from high-stakes assessments have often been used to merely grade and rank schools and students. But a new trend is emerging, according to this brief. Educators are beginning to see the power of using assessment data to improve instruction. This brief discusses ways to use data to improve instruction at the school, classroom, and student levels. It begins with a brief overview followed by discussions on how data-based decisions improve instruction and how the use of assessment data can help to improve instruction. It next discusses the role of the central office. It then presents several examples of effective data use for instructional improvement. The next two sections offer advice on developing and using effective data-based assessment systems, with discussions on staffing, providing sufficient time and resources for staff development, and making sure that decisions are based on "good" data. The brief concludes that the ultimate goal is a system that integrates instruction and assessment into a cycle of continuous improvement that leads to high levels of student achievement. The brief also includes a number of resource reviews, a brief list of online resources, and 26 references. (WFA)