The present study aimed to investigate the associations between teachers' observed emotional support and social competence among Finnish pre-schoolers (6-year-olds). The quality of emotional support was observed using the Classroom Assessment Scoring System Pre-K in 47 preschool classrooms twice across the preschool year. Teachers rated children's social competence in autumn and again in spring, using the Multisource Assessment of Social Competence Scale (MASCS), which produced sum scores for cooperating skills, empathy, impulsivity, and disruptiveness. Consistent with the transactional model, we specified reciprocal (auto-regressive and cross-lagged) relationships within a Multilevel Structural Equation Models (MSEM) framework. The results showed that higher quality of emotional support in preschool autumn was related to more prosocial behaviours typical of the classroom during spring of the preschool year. Children's antisocial behaviours typical of the preschool classroom were not associated with quality of emotional support or vice versa. The results emphasize the importance of responsive and sensitive classroom interactions in promoting prosocial behaviours.