This article deals with issues that are central to changed mathematics pedagogical practice. It engages general debates about teaching reflexivity and within that, more specific debates in relation to identity. It uses theoretical concepts derived from Lacanian psychoanalysis as a way of understanding what structures a teacher's narrative about his practice. Thus, the article is both a study of one teacher's reflections on a sequence of algebra lessons at the secondary school level, and an exploration into a range of theoretical issues about identity construction, about knowing, and about effective practice.