We examined the extent to which dynamic coupling of (a) maternal sensitivity and (b) children's responsive and assertive behaviors toward mothers during a semistructured play session predicts children's responsive and assertive behavior toward an unfamiliar peer at 39 months and a close friend at 58 and 66 months. Maternal and child behaviors were rated in 30-s epochs during play when children were 32 months old (Time 1; N = 128; 66 girls). Children were rated on their responsiveness and assertiveness toward an unfamiliar peer in the early preschool years (Time 2) and toward a friend in the late preschool years (Time 3). Residual dynamic structural equation models showed that stronger positive contemporaneous coupling of maternal sensitivity and children's responsiveness in a given 30-s epoch of the play session predicted greater observed responsiveness toward a friend in the late preschool years, after controlling for mean levels of maternal sensitivity and child responsiveness. On the other hand, positive contemporaneous coupling of maternal sensitivity and child assertiveness predicted children's higher levels of observed assertiveness toward an unfamiliar peer in the early preschool years, after controlling for mean levels of maternal sensitivity and child assertiveness. Results suggest that the dynamic coupling of specific positive behaviors during mother-child interaction may provide children with social scripts to draw on in diverse peer contexts. (PsycInfo Database Record (c) 2024 APA, all rights reserved).