Social interaction, while solving a problem, can favour the appearance of students' proving processes. Insofar as students are committed in finding a common solution to a given problem, they have to come to an agreement on the acceptable ways to justify and to explain their choices. We have shown that proving processes are not the only processes likely to appear in such social situations, and that in some circumstances they could even be almost completely replaced by other types of interactional behaviours. Our point is that in some circumstances social interaction may become an obstacle, when students are eager to succeed, or when they are not able to coordinate their different points of view, or when they are not able to overcome their conflict on a scientific basis . In particular these situations can favour naive empiricism, or they can justify the use of crucial experiment in order to obtain an agreement instead of proofs at an higher level.