A critical engagement with the idea of evidence and the wider idea of evidence-based or evidence-informed education remains important, not least because of the rhetorical power of the idea of evidence. Who, after all, would want to argue that education should not be based upon or at least be informed by the best available evidence? But already here lies a major problem, because by framing the discussion in terms of whether or not we should want to have evidence, two other really important questions – ‘Evidence of what?’ and ‘Evidence for what?’ – easily disappear from sight. With regard to the first question, which we can also phrase as the question about what kind of evidence we are talking about, it is important to see that whereas the notion of ‘evidence’ has a rather broad, perhaps even inclusive meaning, the discussion about evidence in education and similar practices, tends to have a much more precise and specific meaning. In the majority of cases evidence here refers to knowledge about the effectiveness of interventions or, in the often-used lingo, evidence about ‘what works.’ It is here that we can already find a major problem with regard to the idea of evidencebased or evidence-informed education. This problem is not so much a matter of epistemology – that is, whether such knowledge is possible or not and what its status is – as it is a problem of ontology. It has to do with the way in which the ‘working’ of education is understood and thus with the way in which education itself, as a practice and as an act or an activity, is understood