Recently, research into gender differences in achievement has mainly concentrated on the underperformance of boys in comparison with girls. Qualitative research in particular points to the importance of the gender-specific cultures adolescents experience. The purpose of this article is to test quantitatively the explanatory value of academic culture with respect to the stated gender differences in achievement. Use is made of data of 3760 pupils in the third and the fourth year of secondary education in a sample of 34 schools in Flanders (Belgium). A distinction is made between general schools preparing students for higher education and schools offering technical and vocational education. It is demonstrated that boys' culture is less study oriented than girls' culture and that this difference can be held responsible for the gender differences in achievement, at least in general schools. In technical/vocational schools, boys seem to oppose the study culture.