the use of technology is nowadays oflen strongly recommended by institutions and curricula. but on the one hand it turns out that a large part of mathematics teachers remains reluctant of integrating technology into their teaching (guin & trouche 1999). on the other hand several investigations of students using technology that heve been carried out over the past ten years show that students do not learn from simply interacting with technology. the design of adequate tasks, the role of the teacher plays a critical role in the success of integrating tecnology (largrange et al.2001).