Perhaps the most pressing issue concerning teacher education and training since the end of the Second World War has been that of the role of theory--or principled reflection--in professional expertise. Here, although the main post-war architects of a new educational professionalism clearly envisaged a key role for theory--considering such disciplines as psychology, sociology and philosophy as indispensable for reflective practice--there are nevertheless well-rehearsed difficulties about crediting such disciplines with quite the (applied) role in educational practice of (say) physiology or anatomy in medical practice. This paper argues that while recent developments in professional teacher education and training may have moved on from erstwhile instrumentalist and/or applied science (competence and other) perspectives, there may yet be a case for further progress towards a rather more sophisticated philosophical psychology of teacher knowledge and expertise.