From drawing to construction: teachers mediation within the Cabri environment

Abstract. Within the general framework of a long term experimetal project focused on the introduction to mathematical proof, this paper presents the analysis of a collctive disussion taking place in a 9th grade class. The discussion deals with different strategies for constructing a square in the Cabri environment. The analysis has two objectives. On the one hand, to show different phases of the evolution of the justification process - from empirical verification to geometrical argumentation - centred on the shift from checking on the product to checking on the procedure. On the other hand, to relate the evolution of the meaning of justification both with the specific nature of the software and the intervention of the techer.