Purpose: A large body of research finds that unstructured socializing with peers is associated with antisocial behavior. Less attention, however, has been devoted to identifying the sources of unstructured socializing, particularly in the context of accounting for changes in unstructured socializing and how various factors might interact with one another in accounting for such changes. This study extends prior work by examining whether the association between changes in autonomy and changes in unstructured socializing is moderated by changes in maternal knowledge of an adolescent’s whereabouts and activities. Methods: To investigate this issue, we make use of two waves of data from a national sample of U.S. adolescents who participated in the Study of Early Child Care and Youth Development. Results: The positive association between changes in autonomy and changes in unstructured socializing is significantly diminished among adolescents who experience greater increases in maternal knowledge of their whereabouts. This pattern was particularly evident when the focus was explaining changes in weekend unstructured socializing. Conclusions: This study suggests that efforts to assist parents in maintaining or improving awareness of their child’s whereabouts and activities during adolescence could hold promise for reducing unstructured socializing, even as adolescents are granted greater autonomy in decision-making.