This article reports the original evidence-based outcome study on parent-child parallel group-designed Anger Coping Training (ACT) program for children aged 8-10 with reactive aggression and their parents in Hong Kong. This research program involved experimental and control groups with pre- and post-comparison. Quantitative data collection consisted of the Child Behavior Checklist (CBCL), Child Behavior Checklist Teacher's Report Form (CBCL-TRF), and Peer Observation Checklist (POC). Two pilot studies and the main study were conducted. Out of 34 applicants, 18 were selected and divided between two experimental groups and one control group in accordance with the rule of randomization. The effectiveness of the program has been consistently verified in lessening overall childhood aggression, especially for children's physical aggression, but not verbal aggression. (Contains 4 tables.)