Most districts help teachers use data to improve student learning, often supporting this effort with federal funds. But many teachers feel unprepared to use student data to inform their instruction -- referred to as data-driven instruction (DDI) -- and there is little evidence of whether it improves student achievement. This report assesses an intensive approach to supporting teachers' use of student data to tailor their instruction. The report found that this specific approach to DDI did not improve students' achievement, perhaps because the approach did not change teachers' reported use of data or classroom practices. [For the executive summary, see ED598643. For the appendices, see ED598645. For the study highlights, see ED598648.]