using-randomised-controlled-trials-in-educationWe seek to promote an approach to RCTs that is tentative in its claims and that avoids simplistic generalisations about causality and replaces these with more nuanced and grounded accounts that acknowledge uncertainty, plausibility and statistical probability …

Whilst promoting the use of RCTs in education we also need to be acutely aware of their limitations … Whilst the strength of an RCT rests on strong internal validity, the Achilles heel of the RCT is external validity … Within education and the social sciences a range of cultural conditions is likely to influence the external validity of trial results across different contexts. It is precisely​ for this reason that qualitative components of an evaluation, and particularly the development of plausible accounts of generative mechanisms are so important …

Highly recommended reading.