This research shows that self-assessment integrated in teacher education gives rise to changes in the beliefs about assessment and more broadly in pedagogical beliefs. Changes in beliefs are likely to guarantee durable changes in practice. A descriptive model of self-assessment is proposed. Its role in professional training is explored in particular through a session of in-service training for experienced teachers. Transversal and longitudinal analyses of their discourse show how beliefs change and highlight self-assessment. The results show that teachers who change their pedagogical paradigm are those who consciously engage in a process of self-assessment which in turn leads to changes in their vision of the teacher's role.