This article examines how girls' and boys' different peer cultures in middle childhood may set the stage for challenges in emerging heterosexual romantic relationships in adolescence. Two theoretical frameworks are presented for understanding gender differences in children's same-gender friendships and peer groups in middle childhood: the two cultures perspective (Maccoby, 1998) and the emotional trade-offs perspective (Rose & Rudolph, 2006). Emerging empirical evidence is presented to highlight how girls' and boys' gendered friendship qualities may be linked to difficulties girls and boys have when they come together in early romantic relationships. Preliminary longitudinal data are presented that suggest that girls' relational and boys' physical aggression toward same-gender peers in middle childhood may relate to having emotionally intense arguments in early adolescence. Implications for prevention and intervention are discussed.