This paper examines the evolution of the professional identities of student teachers (STs) in a paired-placement teaching practicum in Vietnam. The study draws on activity theory, its notion of contradiction, and Vygotsky's concepts of ZPD and "perezhivanie", to identify the factors driving the intricate learning process. Opportunities for learning were initially manifested in conflicts within the teacher pair, for example negotiation of their multiple identities, as friends, students and teachers in training. However, within the framework of planned and supervised collaboration, the STs resolved most of their conflicts constructively and experienced qualitative development in their teaching identities. (Contains 3 tables and 2 figures.)