This work is part of a larger research project that explores how professional teacher identity is constructed and developed. For the present study, we analysed 22 informal experiences. These experiences have been analysed in terms of their contribution to the formation of professional teacher identity. We designed a qualitative multiple case study in which semi-structured interviews were applied to 26 student teachers. We applied our own form of discourse analysis based on certain discursive markers. Our main findings are that identity change occurs not only through traditional formal experiences, but also through informal experiences and interactions between the two. We propose the importance of what we term informal experiences in establishing connections and driving the formation and development of identity. Finally, we suggest that professional teacher identity serves as an 'adhesive' that unites the various learnings achieved in different contexts over time. We conclude with a discussion in which we propose that identity should be considered an interconnected and subjective phenomenon, rather than a personal resource. We also propose that identity is connected to dialogic aspects involving a sense of collaboration and participation, and that these can be transferred from informal contexts to formal contexts.