The goal was to assess the role of children's social cognitions about peers in attitudes toward school. Because of gender segregation, we differentiated children's cognitions about same-gender and other-gender peers. We examined the influence of gender-based relationship efficacy for both own-gender and other-gender peers (GBRE-Own and GBRE-Other) on school-related outcomes while controlling for other peer relationship variables. Students (N = 206, fourth grade) reported on relationship efficacy, peer relationships, and school outcomes in Year 1 and again 1 year later. Results indicated that efficacy beliefs were positively related to school outcomes. Moreover, a developmental pattern emerged: GBRE-Own consistently predicted school outcomes in fourth grade but not fifth, and GBRE-Other consistently predicted school outcomes in fifth grade but not fourth. As interest in other-gender relationships becomes more prominent in late childhood, efficacy about other-gender interactions appears to exert influence in mixed-gender contexts (e.g., classrooms). Implications are discussed for improving peer interactions and school attitudes.