The Wallonia-Brussels Federation offers teachers assessment tools meant to measure students’ abilities to select and combine, in unusual situations, learnt-in-class procedures. Even though many researchers were involved into scientific reflections on these tools and their diagnostic value, the impact of the contents specifically assessed has not been really considered. The purpose of this paper is to highlight the importance of this aspect through the analysis of a tool related to elementary algebra. While extending the general findings arising from the tool as intended by the authors in the competency-based approach, the results confront the strategies adopted by students when dealing with the different tasks proposed. Beside the specific results to tested task, the paper intends to show the added value of this integrated approach to the competence assessment issue.