The teaching practicum is often considered as a compulsory activity for enculturating new members into the teacher community by providing opportunities to experience teaching in action. However, the practicum is rarely conceptualized in terms of its transformative potential. In this study, we report the results of a two-year ethnography study of a teaching practicum in Brazil based on the {coteaching | cogenerative dialoguing} model. Our study shows that the practicum does not have to be a mere induction experience, but that it also may be the transformative locus for (a) the practicum participants (new teachers, school teachers, teacher educator, and students) and (b) school and university/school relationships, and (c) of the practicum activity itself. The results show the potential of the practicum to transform individual and collective agency. Implications are discussed for reorganizing the teaching practicum.