Fricke et al. and Hagen et al. (2017) each report on large-scale pragmatic randomised controlled trials delivered in schools or nurseries, investigating language interventions for vulnerable children and showing moderate positive effect sizes. Such research is part of a recent development of 'what works' research in England, and the number of "what works" trials continues to increase, largely through funding from the Sutton Trust, who are concerned with disadvantaged children, to the Educational Endowment Foundation (EEF). "What works" research is not firmly accepted by all educationalists, however, results of trials are now available quickly and presented in a manner intended to be accessible to practitioners. This development may facilitate principled decisions on the adoption of interventions by schools, as trials and their outcomes may be interrogated to support decisions on whether the anticipated impact is worth the cost of implementation. [To read the article by Fricke et al., see EJ1154623. To read the article by Hagen et al., see EJ1154627.]