Teaching observation is widely promoted as a mechanism for developing teaching practice in higher education. Specifically, formative peer observation is considered by many to be a powerful tool for providing feedback to individual teachers, disseminating disciplinary good practice and fostering a local evaluative enhancement culture. Despite its widespread use, however, there are still reservations about the extent to which participation in formative teaching observation can contribute to the development of lecturers' critical reflection and the enhancement of practice. In particular, the capacity of colleagues to evaluate and provide critical feedback that can inform a reflective approach to practice has been questioned. This paper presents a single case study of one lecturer's experience of participating in a single teaching observation cycle, conducted with an educational expert and disciplinary peers acting as both observer and observee. Content analysis of written feedback provided after each teaching observation identified five categories of commentary on teaching practice: description, positive reflection, critical reflection, applying reflection and misconception. The analysis reveals a change in the proportion of critically reflective and applied feedback comments before and after the lecturer's experience of participating in developmental teaching observation with an educational expert. We argue that this change in the type of written feedback signals the important role of pedagogic experts in facilitating the development of the lecturer's capacity to evaluate colleagues' teaching through the modelling of critical feedback behaviours. We place this within a recent theoretical framework that proposes a hybrid observation model combining linear and hierarchical discourse of teaching.