What works in educational improvement? Debates about this question have played out in education and other circles for many decades (Cremin, 1988; Kaestle, 1983; Kliebard, 1987). Arguably these debates entered a new era at the turn of this century as the United States Department of Education, private foundations, universities, and others issued various calls for evidence-based approaches to educational improvement and made unprecedented investments in identifying specifi c interventions that might improve student learning-often called “what works” (http://ies. ed.gov/ncee/wwc/; http://dww.ed.gov/). An intensive focus on what works marks an important evolution in education policymaking that for decades promoted educational improvement strategies for a host of reasons other than whether or not they might actually help all students learn at high levels. Some have suggested that this shift is particularly essential to addressing persistent race-and class-based achievement gaps.