It is a pioneering study to reduce reactive and proactive aggression in high-risk children aged 6-10 through an innovative intervention through storytelling. The original storytelling group intervention was based on the social information processing model, specifically tailor-made for the distinctive functions and motives of reactive and proactive aggression. Eighty-seven elementary schools in Hong Kong were recruited through open recruitment, and 15 schools were randomly selected. Four thousand eighty-six children (2,292 boys and 1,794 girls) from Grades 1 to 4 completed the screening, and 371 high-risk students (280 boys and 91 girls) with reactive and proactive aggression were recruited based on the inclusion criteria. We conducted a randomized controlled trial with a longitudinal design. Participants were then randomly assigned to the storytelling intervention, placebo, or control group. The group intervention consisted of 10 weekly 1-hr sessions. The participants were assessed at the baseline, after treatment, and 6 months after treatment by self-report and parent report. Longitudinal data were analyzed by linear mixed models. The results demonstrate the effectiveness of the storytelling group intervention in reducing aggression. Compared with the placebo and control, the storytelling intervention further reduced self-reported aggressive behaviors but not parent-reported externalizing and internalizing problems. This storytelling intervention could be adopted in schools and other settings to treat high-risk children with aggressive behaviors without stigmatization. It can positively impact schools and society by reducing bullying and delinquency. (PsycInfo Database Record (c) 2024 APA, all rights reserved).