This report summarizes the complex research literature on quantitative methods for assessing how impacts of educational interventions on instructional practices and student learning differ across students, educators, and schools. It also provides technical guidance about the use and interpretation of these methods. The research topics addressed include: subgroup (moderator) analyses based on study participants' characteristics measured "before" the intervention is implemented; subgroup analyses based on study participants' experiences, mediators, and outcomes measured "after" program implementation; and impact estimation when treatment effects vary. The focus is on randomized controlled trials, but the methods are also applicable to quasi-experimental designs. [This report was prepared for the Institute of Education Sciences (IES) by Decision Information Resources, Inc. under Contract ED-IES-12-C-0057, Analytic Technical Assistance and Development.]