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Rigorous Large-Scale Educational RCTs are Often Uninformative: Should We Be Concerned?

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JournalEducational Researcher
DateAccepted/In press - 28 Jan 2019
DateE-pub ahead of print - 11 Mar 2019
DatePublished (current) - 2 Apr 2019
Issue number3
Number of pages9
Pages (from-to)158-166
Early online date11/03/19
Original languageEnglish


There are a growing number of large-scale educational Randomized Controlled Trials (RCTs). Considering their expense, it is important to reflect on the effectiveness of this approach. We assessed the magnitude and precision of effects found in those large-scale RCTs commissioned by the EEF (UK) and the NCEE (US) which evaluated interventions aimed at improving academic achievement in K-12 (141 RCTs; 1,222,024 students). The mean effect size was 0.06 standard deviations (SDs). These sat within relatively large confidence intervals (mean width 0.30 SDs) which meant that the results were often uninformative (the median Bayes factor was 0.56). We argue that our field needs, as a priority, to understand why educational RCTs often find small and uninformative effects.

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