Federal education policy in recent years has encouraged state and local education agencies to embrace data use and analysis in decision-making, ranging from policy development and implementation to performance evaluation. The capacity of these agencies to make effective and methodologically sound use of collected data for these purposes remains an outstanding question. As hundreds of millions of dollars are distributed from the federal Department of Education to states developing longitudinal data systems, education leaders approach data use with widely divergent levels of skill and understanding. This paper reviews four guiding principles for education stakeholders as they attempt to use data as a basis for making decisions. These principles draw heavily from experiences and observations of CNA field analysts, who are embedded in state departments of education to provide ongoing technical assistance. The paper's focus is on experiences of field analysts in Tennessee, a state currently implementing a nearly $502 million federal Race to the Top grant-a grant largely won based on the commitment to data use represented by its long-standing value-added assessment system (TVAAS). As in states across the country, Tennessee now confronts a series of challenges in developing data use skills across the state education agency (SEA), local leaders, principals, and teachers, especially as significant portions of principal and teacher evaluation are now tied to student value-added data. The increasing importance of understanding and acting on educational data make clear the need for common guiding principles in their use. The principles include the following: (1) Establish common definitions and understandings of terms; (2) Anticipate potential unintended consequences of data definitions and priorities; (3) Ensure that data definitions are applied uniformly to appropriately homogeneous target populations and disparately to populations that are appropriately heterogeneous; and (4) Disaggregate data in order to reveal the most complete and accurate picture. Based on CNA's work in the state, they present these principles in the use of data for state-level decision-making. In so doing, they intend to inform a conversation about the appropriate role of student and teacher performance data in policy decisions and to prompt deeper research into how state leaders collect, analyze, and act on those sets of data. [This paper was funded by the Independent Research Council at CNA.]