Based on former research, it can be assumed that attachment relationships provide a context in which children develop both the effortful control (EC) capacity and the repertoire of responses to regulate distress. Both are important to understand children’s (mal)adjustment. While the latter assumption has been supported in several studies, less is known about links between attachment and EC. We administered questionnaires to measure anxious and avoidant attachment or trust in maternal support in two samples of early adolescents. EC was reported by the child in Sample 1 (n = 244), and by mother in Sample 2 (n = 177). In both samples, mothers reported children’s maladjustment. Consistent with predictions, insecure attachment was related to reduced EC. Moreover, EC indirectly linked insecure attachment to maladjustment. This study provides evidence that studying EC is important to understand the self-regulatory mechanisms explaining the link between attachment and (mal)adjustment in early adolescence.