In a recent review article, Colliver concluded that there was no convincing evidence that problem-based learning was more effective than conventional methods. He then went on to lay part of the blame on cognitive psychology, claiming that 'the theory is weak, its theoretical concepts are imprecise. the basic research is contrived and ad hoc'. This paper challenges these claims and presents evidence that (a) cognitive research is not contrived and irrelevant, (b) curriculum level interventions are doomed to fail and (c) education needs more theory-based research.