Although theory and preliminary research suggest that maintaining high levels of school belonging promotes positive peer relationships (Juvonen, 2006), there is a need to examine the role of cultural mechanisms (Hernández & Bámaca-Colbert, 2016). Familism cultural values, which emphasize the importance of family as a source of support, are theorized to promote positive peer relationships. We evaluated prospective reciprocal associations between school belonging and peer relationship quality (peer competence, relational aggression), and the moderating role of familism values, using data on a large sample of Mexican origin children (N = 674) assessed annually from 5th to 8th grades. Based on cross-lagged panel models, school belonging had significant associations with later relational aggression, particularly for children with low familism levels; for those endorsing high familism levels, relational aggression levels were relatively low and not predicted by school belonging.