Background: Oral health is closely linked to systemic health, yet preventive oral health education remains insufficient in many low- and middle-income settings. School-based interventions offer a scalable platform for early prevention and long-term behavioral change. Objective: To evaluate the impact of a repeated school-based oral health education and treatment program on oral disease burden and related systemic outcomes over a three-year period in Kathmandu, Nepal. Methods: A quasi-longitudinal community-based study was conducted through annual dental camps at Mahendra Public School and Shee Thangpal Secondary School between 2018 and 2021 in collaboration with Lions Clubs International. Approximately 500 participants were evaluated annually. Standardized oral examinations were performed using dental charting and Palmer notation. Interventions included oral health education, preventive care, and basic treatment services. From the second year onward, audiovisual and small-group interactive learning strategies were implemented. Oral disease prevalence and self-reported systemic complaints were recorded and compared across years. Results: A significant reduction in oral disease burden was observed. Dental caries prevalence decreased from 62% (≈310 cases) in 2018 to 130 cases in 2021, representing a 58.1% reduction. Gingivitis prevalence declined from 38% (≈190 cases) to 80 cases, also reflecting a ~58% reduction. Participants demonstrated improved oral hygiene practices and increased engagement in peer-led education. Additionally, a reduction in self-reported digestive complaints was noted among adult participants. Conclusion: Sustained school-based oral health programs integrating education, prevention, and treatment are associated with significant improvements in oral and systemic health outcomes. These findings support the scalability of community-based dental education models in resource-limited settings.