In recent years, interest has spiked in data-driven decision making in education--that is, using various types of student data to inform decisions in schools and classrooms. In October 2008, the Council of the Great City Schools and American Institutes for Research (AIR) launched a project funded by The Bill & Melinda Gates Foundation that focused on understanding the use of data as a lever for instructional improvement. The study was conducted in four urban districts located in geographically distinct areas. The project had two interrelated objectives: (1) to document and understand current data-use practices across urban school districts in terms of the use and availability of data--in particular, the administration and use of interim assessments; and (2) to generate empirical evidence regarding the relationships between student achievement and data-use practices at the school and classroom levels. To address the first objective, the authors administered surveys to district academic/curriculum coordinators and research directors to obtain a general overview of the state of current practices in using data to inform school- and classroom-level decision making across urban school districts. Following the surveys, the authors conducted a series of case studies of four urban districts, allowing for a more in-depth look at district data use. This report focuses on the second objective: examining the empirical relationships between teacher and principal use of student interim assessment data and achievement on end-of-year accountability tests. In this report, the authors expand on the existing body of literature on the use of interim assessments by examining the extent to which data-use practices (including perceptions about using data) are related to student achievement. The report is organized in three sections. First, the authors review the literature on using data from interim assessments and put forth a theory of action that undergirds their investigation. The theory of action identifies a set of key dimensions of data use and hypothesizes that supporting conditions in states, school districts, and schools can facilitate the effective classroom-level use of data to respond to students' instructional needs. Second, they report results of an empirical test of this theory of action. The analyses examined the relationship between teachers' and schools' use of interim assessment data and improvements in student achievement in reading and mathematics at grades 4, 5, 7, and 8. They focused on classroom-level data-use practices as reported by teachers, and school-level data-use practices and perceptions as reported by principals. The analyses include more than 1,500 teachers and 150 school principals and student achievement data from over 60,000 students across four urban districts collected during the 2009-10 school year. In the third and final section of this report, they interpret the study findings and provide recommendations and conclusions. Appended are: (1) District and State Context; (2) Measures and Data-Use Survey Items; (3) Information on Samples; and (4) Estimation Methods and Hypothesis Testing. (Contains 77 tables, 9 exhibits and 16 footnotes.) [For "Charting Success: Data Use and Student Achievement in Urban Schools. Executive Summary," see ED536740.]