Background: KidNET has demonstrated favourable outcomes in reducing PTSD symptoms and its comorbid disorders among adolescent refugees. However, the outcome of KidNET in reducing PTSD symptoms in non-refugee adolescents has not been documented. The purpose of this study was to investigate the effectiveness of KidNET in reducing PTSD symptoms among adolescents in secondary schools. Methods: A quasi-experimental research design was used to conduct the study. A total of 120 respondents took part in the study. The participants had a mean age of 15.84 years (SD = 1.01). A Socio-Demographic Questionnaire (SDQ) and the Child PTSD Symptom Scale-V-Self Report (CPSS-V-SR) was used to assess for PTSD symptoms. Results: Independent groups’ t-tests were used to detect significant mean differences whilst Cohen D (d) was used to determine effect sizes. At endline, a between-groups t-test showed a medium effect size (d=0.68). A significant difference between the groups was also established at p=0.001. The findings further showed that 38.3% of the participants in the experimental group vs 8.3% in the control group reported a reduction of PTSD symptoms from mild/moderate symptoms at baseline to minimum PTSD symptoms at endline. The findings also showed that KidNET reduced PTSD symptoms in 81.7% of the experimental group. An analysis of the PTSD symptom criteria that showed significant symptom reduction in the criteria for: arousal and reactivity alterations, avoidance and, the criteria for mood and cognitive alterations. Conclusion: The findings showed that KidNET was effective in reducing PTSD symptoms among non-refugee boys in secondary schools.