Casyopee is an evolving project focusing on the development of both software and classroom situations to teach algebra and analysis at upper secondary level. In this article, we sketch the rationales for the Casyopee project in relationship with the focus on functions in upper secondary curricula. To evaluate Casyopee's contribution, we present and analyse an experimental teaching unit carried out in the ReMath European project focusing on the approach to functions via multiple representations for the 11th grade. (Contains 2 figures and 6 notes.)