The main focus of the PÉPITE project is how to build a system that helps teachers to assess students in elementary algebra. We describe here prototypes yet tested in actual classrooms and we share our experience of designing practically useful classrooms tools in a participative way. The methodology adopted is a combination of work in mathematics education and user-centred design derived from Human-Computer Interaction research. Starting from a multi-dimensional model of competence in algebra that includes quantitative and qualitative descriptions, we first show how it is applied to analyse both paper-and-pencil tasks and computerised tasks, and secondly how it is applied to analyse the students’ productions when performing those tasks. Then we present the prototypes developed to automatically build students’ profiles. Finally we discuss the validation process of such an assessment system and our research results.