Bullying is reported to be one of the most prevalent forms of violence in schools and has negative health, financial, and social outcomes. Researchers define bullying as (a) aggressive behavior that is (b) repeated over time and that involves (c) a real/ perceived imbalance of power. The literature on bullying is limited due to the absence of functional behavior assessment procedures and individualized interventions for bullying behaviors. Study 1 developed the Functional Assessment of Bullying Behaviors in Schools (FABB-S) tool. Following expert review 21 items were found to have content validity. Following revision, the items were reviewed by child work groups and were all found to have face validity. Study 2 evaluated the effectiveness of the FABB-S to lead to reductions in aggression toward peers. Direct observation and staff daily rating data indicated that one participant’s problem behavior showed initial signs of decrease following intervention, a second participant’s problem behavior showed increased stability throughout intervention, and a third participant’s problem behavior showed signs of decrease at the beginning and ending of the intervention phase. Social validity data indicated that student and staff participants found the FABB-S and selected interventions to be effective and acceptable. Discussion includes limitations and area for future research.