This article presents the first results of an investigation in a scholastic context aimed a determining the conditions that favour the acquisition of knowledge in biology within interactions in groups of 4 pupils. There were three work sessions in small groups, and some sessions in class groups. The pupils' conceptions were assessed at the beginning and the end of learning as well as at the beginning of the first and second group sessions. The pupils had to compare their ideas and draw one or several pictures with a caption or some sentences to explain if necessary. Interactional analysis showed that the co-development-type interactive dynamics (according to Gilly) contribute to constructing the conceptual field studied owing to the questions the pupils ask one another. Conflicting comparison-type dynamics are beneficial providing that each pupil does not put forward only arguments that contribute to confirming his own opinions. Moreover, it seems that the quality of the interactions depends on the tasks the pupils are requested to accomplish. (Contains 6 figures, 2 tables, and 6 notes.)