This theoretical study examines the mentoring situation and how it might be adjusted to contribute optimally to building pre-service teachers' competences. The study first presents an original theoretical conceptualisation based on which the dynamics of competence building is defined. This conceptualisation is then empirically illustrated and a discussion follows on how cooperating teachers can organise mentoring activity to more effectively support the self-development of pre-service teachers. Last, we argue that a principle of continuity is needed rather than the strict alternation between teacher education at the university and training in the schools.