International audienceWhen learning mathematics, mistakes can serve as productive occasions if a mistake is followed by a process of negotiation and insight. This paper addresses the question of the extent to which the informal occasion of a "mistake" leads to productive interactions in inclusive mathematics classrooms. Within the context of the project LUIS-M video-based qualitative analysis of cooperative learning situations in inclusive classrooms are made with focus on formal and informal occasions for productive interaction. In the paper the negotiation processes which follow mistakes are exemplified and discussed with respect to opportunity for learning processes