Our research focuses on the difficulties students encounter with the learning of calculus, considering that they have to cope with much more mathematical objects but also with new ways of reasoning – not only algebraic calculation, but also the practice of approximation, and a scaffolding way of using functions, limits, derivative, integrals, etc. for proving. The semiotic facet of new objects, and the way to manage it, is also a source of great difficulties. We use a model (Bloch & Gibel, 2011) to describe students' work when they have to deal with the resolution of exercises about parametric curves and differential equations