Preschoolers' (M[subscript age]=48.7 months) social breadth (the number of peer children interact with and the frequency of these interactions) and the relations between breadth and externalizing behaviors were examined using the Q-connectivity method. After considering age, sex, and classroom effects on social breadth, children's externalizing behaviors were studied in relation to levels of social breadth across variations in frequency of exposure to peers and to patterns of decline in social breadth. Externalizing preschoolers occasionally interacted with most of their classmates. However, their individual peer networks moderately to rapidly became selective, and they engaged in repeated interactions with a relatively small number of peers. Although there were no sex effects, significant age and classroom effects were obtained.