The basic premise that social cognitions guide behavior (aggression) was evaluated within relationships marked by dislike. At Time 1, a disliked target was identified for each participant (195 fifth-grade children; 109 boys; 11–12 years old at Time 1) who then responded to questions about different aggression-supporting social cognitions with regard to the chosen target. In addition, aggression directed at the identified peer (from the disliked child’s perspective) was measured twice over a one-year interval. Our results show that aggressogenic thought predicts increases in aggression only when the target is chronically disliked. Moreover, within chronically disliked relationships, the actualization of aggressogenic thought is maximized when children have high initial levels of reactive (in the case of hostile attributions) and proactive aggression (in the case of self-efficacy beliefs), and when targets are initially high on reactive aggression. These findings suggest that social cognitions, assessed within a specific relationship context, can have more predictive validity than traditionally used decontextualized measures.