French students in grades 4 and 5 in schools around Paris wrote explanatory texts in L1 following a lesson in the Life Sciences, four times over the course of the school year. Each session included written correspondence with another student; half the students (Group G1) made suggestions about ways to improve the drafts of the other half of the students (Group G2). All students then revised their text. The results show: (1) an improvement in the quality of the texts produced over the year, even at the first draft stage; (2) greater progress for the students who gave suggestions compared with those who received them; and (3) a fragility of the performance of the last writing session. The results are interpreted in light of the concepts of knowledge transformation strategy and dialogism. The "stepping back" encouraged by adopting the role of tutor to a fellow student may have allowed Group G1 students to build knowledge about explanatory texts and better "orchestrate" the different voices present in their texts. The difficulty of the last writing session, which required a conceptual transformation and a reorganisation of the information provided by the lesson, could explain the poorer performance observed in this session. (Contains 4 tables and 14 notes.)