This study examined the longitudinal relations of mother–child affect exchanges at 18 months with children's mastery motivation at 39 months. Observation and questionnaire data were collected from mother–child dyads when children were 18 months; 43 mothers again rated their children's mastery motivation at 39 months. Results suggested that after controlling for gender and the corresponding 18‐month mastery aspect, positive affect exchanges had long‐term positive relationships with children's persistence and competence, whereas dismissed affect exchanges had long‐term negative relationships with children's persistence and independent mastery. Findings suggest that children's autonomous mastery‐oriented endeavours have deep roots in their early mother–child affective interactions. Copyright © 2013 John Wiley & Sons, Ltd.