Gender segregation is ubiquitous and may lead to increased bias against other-gender peers. In this study, we examined whether individual differences in friendships with other-gender children reduce gender bias, and whether these patterns vary by gender or ethnicity. Using a 1-year longitudinal design (N = 408 second graders [Mage = 7.56 years] and fourth graders [Mage = 9.48 years]), we found that, across groups, gaining more other-gender friendships over the year led to (a) increased positive cognitive-based attitudes toward the other gender and (b) increased positive and decreased negative affect when with the other gender. We also tested the reverse pattern and found support for a bidirectional link. Girls and Latinx children often showed more gender bias than did boys and European American children. Implications for promoting positive relationships between girls and boys are discussed.