A Cochrane review included 56 studies. Aggressive behaviour (assessed as reported or observed aggressive behaviour and school responses to aggression, such as referrals to the headteacher) was significantly reduced in intervention groups compared to no intervention groups immediately post intervention in 34 trials with data (SMD = -0.41; 95% CI -0.56 to -0.26). This effect was maintained in the seven studies reporting 12 month follow-up (SMD = -0.40, 95% CI -0.73 to -0.06).
Comment: The quality of evidence is downgraded by poor methodology of the studies.