Research Findings: In the present study, we investigated the roles of children's social competence and immigrant background in the prediction of the quality of children's relationships with peers and teachers and school adjustment. Participants were N = 212 children (M[subscript age] = 58.32 months, SD = 10.72; n = 98 with an immigrant background) and their teachers (two per class). One teacher in each class assessed children's social competence and behavior problems, whereas the other rated the quality of their attachment relationships with the children and their adaptation to school. Social acceptance was assessed via peer sociometric nominations. Among the results, children with an immigrant background evidenced greater conflict and dependence in their relationships with teachers, poorer social acceptance, and less pleasure in school. Among children with an immigrant background, externalizing behaviors were associated with conflict in relationships with teachers, whereas internalizing behaviors were associated with dependence. Practice or Policy: The study highlights how social behaviors and immigrant background can affect the quality of attachment relationships with teachers in the preschool classroom.