Smile Synchrony Predicts the Quality of Children's Peer Interactions

Positive peer interactions are fundamental to children's social and academic development, yet the dynamic behaviors that support these interactions remain poorly understood. Smiling is one of the most frequent and socially functional behaviors, and when children respond to each other's smiles (smile synchrony) it provides a window into their engagement and connectedness. Although previous work has examined smile synchrony in dyadic settings, little is known about how it shapes perception of group activity or how individual backgrounds and relationships contribute to these dynamics. Here we show that smile synchrony serves as a behavioral marker of group interaction quality in children's collaborative activities. We analyzed facial expressions of 187 children in 34 groups during two everyday educational activities: listening to a story and discussing it together. Using automated smile detection and event-based analysis to quantify directional smile synchrony, we found that children with higher and more evenly distributed synchrony perceived more positive group climates, characterized by greater safety, contentment, inclusion, collaboration, and cohesion. Individual and dyadic factors further modulated these dynamics in activity-specific ways. During listening, synchrony increased with gender and national identity similarity and with perceived closeness to the smile emitter. During discussion, synchrony was heightened among extraverted children, those reporting greater group closeness, and friendship pairs. These findings reveal that smile synchrony captures meaningful variation in children's social engagement during real-world group interactions and reflects the interplay of personality, interpersonal relationships, and social identity. Our results suggest that smile synchrony represents an accessible behavioral marker for assessing peer interaction quality in collaborative learning environments.