This article outlines and appraises the considerable criticism of educational research, both in the United Kingdom and in North America, and shows how it has pointed to a narrowing of what counts as good or worthwhile research in the policy discourse. In particular, this involved prioritising research that purports to show clearly and unmistakably "what works", and institutionalising this view of research in a range of centres that receive official approval. The article, though recognising the fruit of such centres, challenges the epistemological basis of such a narrowing of what counts as research, and, in doing so, analyses what is meant by evidence, the different kinds and strengths of evidence and the consequent need to democratise the search and appraisal of evidence in the constant refinement and criticism of the evidence.