This article presents a model to describe mathematical exercises with educational elements. It enables to specify the alignment between resource and curricula, to precisely describe the knowledge at stake in an exercise, and the way this knowledge is intended to be used. To build this model, we use a reference praxeological model represented using T4TEL. We define a task model as well as the optimum type of tasks notion. This model and its use are illustrated on examples related to school algebra. The advantages and limits of the model are discussed at the end of the article, before suggesting perspectives on their evolution and use in mathematics education research and teacher training.