Quantitative mixed models were used to examine literature published from 1966 through 2016 on the effectiveness of Direct Instruction. Analyses were based on 328 studies involving 413 study designs and almost 4,000 effects. Results are reported for the total set and subareas regarding reading, math, language, spelling, and multiple or other academic subjects; ability measures; affective outcomes; teacher and parent views; and single-subject designs. All of the estimated effects were positive and all were statistically significant except results from metaregressions involving affective outcomes. Characteristics of the publications, methodology, and sample were not systematically related to effect estimates. Effects showed little decline during maintenance, and effects for academic subjects were greater when students had more exposure to the programs. Estimated effects were educationally significant, moderate to large when using the traditional psychological benchmarks, and similar in magnitude to effect sizes that reflect performance gaps between more and less advantaged students.

Most evaluators have embraced the goal of evidence-based practice (EBP). Yet, many have criticized EBP review systems that prioritize randomized control trials and use various criteria to limit the studies examined. They suggest this could produce policy recommendations based on small, unrepresentative segments of the literature and recommend a more traditional, inclusive approach. This article reports two empirical studies assessing this criticism, focusing on the What Works Clearinghouse (WWC). An examination of outcomes of 252 WWC reports on literacy interventions found that 6% or fewer of the available studies were selected for review. Half of all intervention reports were based on only one study of a program. Data from 131 studies of a reading curriculum were used to compare conclusions using WWC procedures and more inclusive procedures. Effect estimates from the inclusive approach were more precise and closer to those of other reviews. Implications are discussed.

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