Teaching proof in a dynamic geometry environment: what mediation?

Abstract : This paper aims to discuss two issues. First we intend to analyse if and how dynamic geometry software prove to be a communication space for students and how they support students towards proving. Second, we reflect about the use of video-tapes as source of information both for Mathematics Education research and for the teaching practice. In particular we approach the question: how do video-tapes help in the construction of a shared experience in the classroom?