Student school performance can be related not only to cognitive aspects, but also to the whole set of habits, behaviours and values triggered in the school environment. These involve some heterogeneous components concerning the cognitive, subjective, cultural and linguistic spheres underlying student activity in class, particularly when dealing with reading and writing. The article shows how this theoretical approach focusing on the influence of students’ school and non-school socialisation habits may be useful in explaining the gap between results achieved by French students in the tests within the international Pisa survey focusing on reading comprehension skills. The analyses illustrated in the article largely confirm the hypothesis concerning the heterogeneity of the students assessed. The conclusions arrived at in the article concern various spheres: the Pisa study, the analysis of the task given to students, and the components of the gap in school performance.