Parents and school staff play important roles in promoting children's oral health. Our study goals were to investigate whether an intervention targeting parents and school staff can improve the oral-health behavior and oral-health status of schoolchildren. Three-hundred and ninety-two schoolchildren in six schools in Tehran participated in a group randomized trial from September 2010 to March 2011. Schools were randomly allocated into three groups: comprehensive, student, and control. Intervention in the comprehensive group consisted of strategies to encourage children, their parents, and school staff to increase the frequency of toothbrushing and flossing. In the student group, the intervention targeted only children. The control group received no intervention. The primary outcome was change in oral-health behaviors (brushing and flossing), while the secondary outcomes were changes in oral hygiene and Community Periodontal indices and in Health Belief Model components. Multilevel modeling was employed for data analyses. Students who were in the comprehensive intervention group brushed and flossed significantly more frequently compared with those in the student intervention group. Although students' gingival health improved significantly in the comprehensive intervention group, such significant improvement was not seen in the student group. In conclusion, promising results are seen when the oral-health education targets both school and home settings.