This study analysed the relationships between (a) the nature of the interactions between preservice teachers and their cooperating teachers and (b) the knowledge that the teachers constructed, validated or invalidated during post-lesson interviews. Six interview excerpts, chosen as having been particularly instructive, were analysed from the perspective of the semiotic theory of the course-of-action (Theureau, Le cours d'action: analyse semio-logique [The course of action: A semiological analysis], Berne, Peter Lang, 1992). The results showed that the knowledge constructed, validated or invalidated most concerned the pedagogical contents when the teachers shared the same concerns, the same expectations, and at least a part of the same knowledge being mobilized and/or constructed. The conditions for effective professional collaboration are discussed.