Twenty-six studies (n=24,246, where stated) were included in the review. The studies were mainly pre-test post-test studies with control groups that may or may not have been chosen randomly. In addition, 7 randomised controlled trials (RCTs), one randomised matched-pairs study, 2 cohort studies and 2
quasi-experimental studies were included. Units of allocation and analysis varied between and within the studies, including individual children, classes and whole schools. The majority of the studies were conducted in either the USA or Europe.
Curriculum interventions (10 studies).
The studies reported inconsistent decreases in bullying and several reported an increase in bullying associated with curriculum interventions. Six of the studies reported no significant improvements in bullying. Of the 4 studies that did show less bullying and victimisation in the intervention group, three also showed bullying increased in certain populations or with certain measurement tools.
Whole-school, multidisciplinary interventions (10 studies).
Two studies evaluated the Olweus Bullying Prevention Program in primary and secondary school children. One study, conducted by Olweus, reported beneficial effects of the programme; the other
reported increased bullying in the intervention group. Of the remaining 8 studies, seven (six of primary schools and one of primary and secondary schools) reported positive outcomes associated with the intervention group. Five of these studies reported decreases in bullying or victimisation, while the other
two only reported indirect outcomes.
Social and behavioural skills group training interventions (4 studies).
One study of third-grade students reported that social-skills group training resulted in a decrease in aggression, bullying and antisocial affiliations for previously aggressive children. The remaining 3 studies in older children (two of bullying victims and one of aggressive children) failed to result in clear changes
in outcome associated with the intervention group.
Other interventions (2 studies).
One study of increasing the number of school social workers focusing on problem behaviours, including bullying, reported a significant decrease in bullying amongst primary schoolchildren but a worsening amongst secondary schoolchildren. Self-reported thefts, truancy, fighting and drug use also improved
significantly. Another study assessing a mentoring programme for 'at risk' children reported that the intervention was associated with significantly fewer reports of bullying, physical fighting and feeling depressed in the preceding 30 days.