A low-performing California school district experienced a dramatic turnaround when faculty members began studying student assessment data and working together to ensure students had the support they needed. Sanger Unified School District began its reform journey in 2004 when district leaders launched an effort to focus deliberately on student data. Teachers and administrators received training in instructional strategies, and the district began assessing students more regularly so that teachers and students would know where they stand. Teachers participate in professional learning communities to group and regroup students on the basis of assessment data. This approach has improved student performance across the district, with especially strong improvement appearing among English language learners. (Contains 1 endnote.)