This paper builds on my previous research, explaining the differential achievement of boys and girls in secondary education by the fact that boys' culture is less study orientated than girls' culture. The central question of the present paper is whether the presence of girls at school affects the boys' study culture and, by consequence, boys' achievement. The research is based on data of 877 boys and 714 girls, attending the fifth year of a sample of 15 general secondary schools. It is shown that the gender context of the school does not affect the boys' study culture, but the presence of girls positively influences the general pupils' study culture. By means of multilevel analyses (HLM), it is demonstrated that the larger the proportion of girls at school, the higher the boys achieve, and this finding can be ascribed to the general pupils' study culture.