This article addresses the theme of assessment through the prism of two different approaches to the international PISA assessment. The first approach focuses on the understanding and solving of PISA science items by students of different academic performance and socio-economic and cultural levels in the context of France. In the second approach, PISA is used to expose how mathematics didactics, essentially equipped by the theory of didactic situations and the anthropological theory of didactics, allows to question the notion of evaluation considered as a process and is situated in the context of French-speaking Belgium. The discussion is structured around three points: the epistemological depth of the assessment process, assessment as a tool for analysis and understanding in order to better deal with the heterogeneity of learners, and the place of teachers within the assessment process.