Research on Swedish school children has found that boys tend to be overconfident about their grades in mathematics, while girls tend to be underconfident. We find similar results for El Salvadorian children. Mathematics is considered a masculine task and we show that these findings do not carry over to a gender neutral task (social science), where both sexes tend to be overconfident. We find that girls in a single-sex school are more underconfident in their mathematics abilities than girls in a co-ed school, which may suggest that gender stereotypes become reinforced in single-sex environments.