Démarche expérimentale, validation, et ostensifs informatisés. Implications dans la formation d’enseignants à l’utilisation du logiciel cabri geometre en classe de géométrie

We study the difficulties that teachers experience in learning to use Cabri in their teaching, as several studies have revealed, in order to improve teacher’s training. We use a triple theoretical frame, with the Anthropological Theory of Didactics (Chevallard), the Instrumental Approach (Rabardel) and the Theory of Situations (Brousseau). We have implemented a long ingeniery, with an intensive course about geometric problem solving with Cabri, a period of coached practice, an intensive cours about teaching with Cabri, and a period of coached practice. We show that cabri’s new ostensive objects require a praxeological reconstruction to assimilate the dynamics and the complexity and richness of relations among objects, and that despite a good assimilation of a mathematical praxeology, teachers experience difficulties in practising a didactic praxeology based on validation.