The Incredible Years parent and classroom interventions were evaluated for the first time in elementary schools. Culturally diverse, socioeconomically disadvantaged schools were randomly assigned to intervention or control (CON). In intervention schools, all children received a 2-year classroom intervention beginning in kindergarten. In addition, indicated children were randomly assigned to also receive parent training (PT + CR) or only the classroom intervention (CR). PT + CR mothers reported that, following intervention, children showed fewer externalizing problems and more emotion regulation than CR or CON children. Observations showed that child-mother bonding was stronger in the PT + CR condition than in the CON condition, and PT + CR mothers were significantly more supportive and less critical than CR or CON mothers. Teachers reported that PT + CR mothers were significantly more involved in school and that children in the PT + CR and the CR conditions had significantly fewer externalizing problems than in the CON condition.