We use survey data from the USA and Japan to investigate whether having leader positions at middle and high school as well as participating in sports and clubs is affected by the gender composition of siblings. We find that having only sisters at age 15 increases substantially the probability of school leadership in the USA but has no statistically significant effect on leadership in Japan. We also find that parental education matters more for these behaviors in the USA than in Japan, and that in the latter country the oldest sons or daughters are more likely to be leaders in school.