Research Findings: We tested whether a universal classroom peer pairing intervention -- "Buddy Up" -- would strengthen dyadic peer interactions among preschoolers (N = 140; M[subscript age] = 56.49 months; 53.6% boys; 77.9% Latinx). The "Buddy Up" intervention was informed by Intergroup Contact Theory, which specifies the benefits of exposure to heterogeneous others. Teachers buddied children with other-gender peers. We hypothesized positive intervention effects on the quality of dyadic interactions overall and for other-gender interactions specifically. We also considered whether the effects would generalize (secondary transfer effects) to interactions with other-language peers (English and Spanish). Using a quasi-experimental design, we found intervention effects on improved peer interactions overall and for other-gender dyads. There was little evidence of improved interactions for other-language dyads. Same-gender dyads (notably girl-girl dyads) and same-language dyads (notably English-speaking dyads) also responded positively to the intervention. The use of dyadic peer interaction data during preschool represents an innovative feature of this study. Practice or Policy: "Buddy Up" facilitated positive peer interactions. This is a key building block through which social skills are built and friendships can grow. The findings suggest that early childhood teachers can successfully support students in developing relationships with peers.