In Reply: Dr Wong notes the limitations of quantitative syntheses in education, inasmuch as the study designs, interventions, participants, institutional contexts, and outcomes all represent sources of heterogeneity. These reviews, therefore, often fail to permit strong causal inferences. Realist reviews1 and other systematic efforts to summarize disparate sources of evidence will provide important insights beyond a pooled estimate. We think, however, that such heterogeneity need not remain the norm in the future. On the contrary, as researchers work collaboratively using common theoretical frameworks, intervention definitions, and outcomes, we expect evidence will accrue that can be systematically synthesized to illuminate practice and advance theory.