Drawing on sociocultural psychology, the clinic of activity and discourse analysis, this study analysed a session of health education that brought together a nurse, Inès, and an adolescent living with diabetes. It aimed, first, at investigating the mechanisms of shared understanding and reciprocity involved in explanations, second, at bringing about professional development. It analysed an explanation sequence and in a second step used a method that confronted the nurse to her activity (method of simple and cross self-confrontation). Results showed that in the session of health education, medical discourse tended to dominate, and created a strong asymmetry between the participants, thus raising doubts about the patient’s comprehension. Whereas in the simple self-confrontation Inès’ comments focused on the patient’s comprehension and emotional states, in the cross self-confrontation, her colleague’s comments led her to question her own emotional states and interpretations. The method of self-confrontation seems then adequate to capture the psychological mechanisms underlying the explanations provided by practitioners and to foster a form of professional development.