The scientific literature emphasizes the importance of multiple tests, or replications, of studies to ensure that conclusions are accurate. Over the last five decades, there have been many studies of Direct Instruction’s efficacy, and researchers have reviewed and summarized this vast literature. They have found strong and consistent evidence of DI’s effectiveness.
Two approaches are typically used in such analyses: systematic literature reviews and meta-analyses. Both approaches begin with a delineation of the topic to be covered. For instance, some have looked only at studies of reading or of mathematics. Some have focused on studies of whole school reform. Some may look only at special populations, such as students with disabilities. Systematic literature reviews and meta-analyses may also use methodological criteria to limit the range of studies examined, such as sample size or the nature of the research design. Once the researchers have determined the topic and criteria to be used, they try to amass all the relevant studies and then carefully examine their findings.
The procedures used to summarize the findings differ slightly for the two approaches. Systematic literature reviews usually involve narrative summaries of the results. They describe the nature of each study and compare and contrast conclusions. These reviews usually include simple tallies of the outcomes, noting the proportion of results that are positive, negative, or indeterminate. Meta-analyses use a more statistical approach. They translate results into a common numerical metric, usually an effect size, and statistically analyze variations in the metric and factors that might influence it.
All of the literature reviews and meta-analyses of Direct Instruction materials have found strong evidence of their effectiveness.
