This study demonstrated the existent role of contingent teacher attention in maintaining a preschool child's aggression to his peers, as well as an imposed use of contingent teacher attention to increase his low peer interaction. Aggression and peer interaction were analyzed independently as two baselines of multiple baseline design; each was subjected to at least one reversal. The multiple baseline design was used to examine three possibilities: (1) that the high rate of aggressive behavior was in itself impeding the emergence of peer interaction; (2) that contingent teacher attention could be used to maintain a reduced rate of aggressive behavior; and (3) that a similar use of teacher attention could maintain an increased rate of peer interaction. The technique of largely ignoring the subject's aggressive behavior and attending instead to whatever child he was attacking decreased his aggressive behavior to an acceptable rate. Two reversals of this technique displayed experimental control, each recovering the high baseline rate of aggression. After the aggressive behavior was decreased for the final time, teachers attended to the subject only when he was involved in social interaction with peers, and they thus increased his social interaction to a high rate. Later, they withdrew their attention for social interaction and reversed the effect and finally then recovered it.