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In this article, several ways to adjust gross school effects are discussed to set the stage for estimating treatment effects in schooling. Although it is quite hazardous to hypothesize realistic benchmarks for results from meta-analyses, because of the dependency of effect sizes on subject matter area, grade level, and study characteristics, a treatment effect of d = .20 can be considered as educationally meaningful. Commonly addressed effectiveness-enhancing school factors show much inconsistency across meta-analyses and frequently small effects (in the order of d = .10). An analysis of the conceptual and methodological foundations of defining and measuring treatment effects in schooling indicates that flaws in the measurement of treatments could be an additional cause of small effect sizes in educational effectiveness research. Results of this review are analysed from the perspective of “limited malleability” in educational effectiveness.
Jaap Scheerens (Fri,) studied this question.