This article argues for its central construct – that of transformation – to be understood by teachers and teacher educators in psychological terms. Transformation requires teachers to fashion disciplinary knowledge such that it is accessible to the learner. It is argued that for transformation to happen, teacher thinking must include a sophisticated grasp of cognition and metacognition if teachers are to be characterised as competent, let alone expert. This paper is written within a context of considerable social and academic scrutiny in the UK of the form and content of professional teacher preparation and development.