Having leader positions at school, as well as participating in sports and clubs helps promoting valuable non cognitive skills, including leadership, self-discipline, motivation, competitiveness and self-esteem. We use survey data from the US and Japan to investigate whether these behaviors in middle and high school are affected by the gender composition of siblings. We find that having only sisters at age 15 increases substantially the probability of school leadership both for males and for females in the US and the probability of sport participation for males in Japan. We also find that parental education matters more for these behaviors in the US than in Japan, and that in the latter country the oldest son or daughter are more likely to be leaders in school.