Producing an explanatory proof in a 9TH grade classroom

Résumé

This paper presents part of a study that deals with the problem of proof in schol-arly mathematics. It describes the way in which four students in 9th grade explored a task related to the discovery of symmetry axes in various geometric figures. The proof constructed by them had essentially an explanatory function. The teacher’s role in meaning negotiation of proof and its need is also analysed. One outcome discussed here is that students develop first a practical understanding with no awareness of the reasons underlying mathematical statements and after a theoretical one leading them to a construction of proof.