Same difference? Understanding variation in the estimation of effect sizes from educational trials

By applying four analytic models with comparable outcomes and covariates to a dataset of 20 outcomes from 17 educational trials, we found results closely matching in well-powered studies without serious implementation problems. The interventions and evaluations were all funded by the Education Endowment Foundation and independently evaluated. We demonstrated that when an analysis takes little account of research design, or where there were difficulties with implementation and data collection, point estimates of effect differ and estimates of precision vary. This adds to the challenge of understanding the comparative impact of interventions and deciding which are worth scaling up.