This study explored longitudinal associations between student-teacher closeness in Early Childhood Education and Care (ECEC) at 5 years of age and children's externalising problems at 3, 5 and 8 years, and its potential dependency on teachers' perceived competence regarding children's behavioural and social problems. We applied structural equation modelling to data from 7478 children (50.2% boys) from the Norwegian Mother Father and Child Cohort study. Results show that teachers' reports of close relationships in ECEC are beneficial for reduced externalising problems at 8 years, as reported by mothers. Yet, early externalising problems at 3 years compose a risk for low closeness in ECEC. Insufficient competence among teachers about children's social and behavioural problems increases this risk, especially in the presence of student-teacher conflict. When teachers perceive their competence as sufficient, the risk of low closeness is reduced for these children.