Introducing students to geometric theorems: how the teacher can exploit the semiotic potential of a DGS

Abstract. Since their appearance new technologies have brought a lot of expectations about their potential in innovating teaching and learning practices, in particular any didactical software, such as a DGS (Dynamic Geometry System) or a CAS (Computer Algebra System), has been considered an innovative elements and its introduction an innovation in the classroom practice. This paper intends to present a theoretical framework modeling the teaching learning process mediated by an artefact, and show show the use of a DGS can be exploited by the teacher to innovate teaching and learning of classic Geometry. The teaching and learning model is illustrated by examples drawn from a long-term teaching experiment carried out in the 9th and 10th grades of a scientific high school. The semiotic potential of a specific artefact, the Dynamic Geometry System Cabri- Géomètre (Laborde and Bellemain, 1993-1998 ), offered the possibility of revisiting the classic notion of Geometric Construction from an innovative perspective.