Résumé
The research presented here builds on an experimental work ran at the end of primary school (9-10 y. o. children) about line symmetry. We intend on questioning the factors that drive the evolution of geometrical activity of students and analyze in that purpose the articulation between student's and teacher's activity. We try to highlight the fact that learning in geometry relies on both an adaptation process when confronted to a task (individual and adaptationist dimension) and a collective and social construction mediated by interactions between teacher and students and between students.