During their teaching practicum future teachers become acquainted with the rights, duties and obligations of their profession in their trajectory of building a teaching identity. In this process, they go through a number of critical incidents, where we observe that student teachers struggle to integrate the meaning of these incidents with their ideas about the imagined teacher and their own perceived identity. The detailed analysis of discourse generated by two pre-service teachers, grounded in the theory of Communities of Practice and in the theory of meaning called Positioning Theory, allows us to understand how a crucial period in the building of a teaching identity evolves through the seeking of creative solutions to the dilemmas and conflicts they face in their daily interactions with students, teaching colleagues, and the practicum supervisor. In this article we argue that the imagined professional identity that the next generation of teachers forges, far from making them more vulnerable, can become a powerful impetus for innovation and educational change.