Through their organization and curricula, schools either promote separate roles for males and females or operate to minimize differences. This study describes sex differences in science and reading achievement and attitudes for nationwide samples of 14-year-old children in the United States, Sweden, and England. There are largely the same sex differences in all three countries: Male and female pupils have similar reading skills, while girls have more positive reading habits; males outperform females in science, with the smallest difference observed for biology; males have more positive attitudes toward science, except that females believe science to be at least as important a topic as boys do. There is no noteworthy increase in sex distinctions with one more year of schooling, from grade 8 to grade 9. However, in English coeducational schools, girls show a deceleration in science and vocabulary achievement relative to their male peers. Girls in English one-sex schools exceed their male counterparts in reading and several science subjects. It is hypothesized that the role of successful female teachers and peers, and the absence of social pressure from boys, may facilitate girls' learning in these areas. A study is proposed of specific school practices and the ways in which they determine sex discrepancies.