Background The school is primed as an avenue for promoting health among adolescents. Conversely, the high unmet dental needs among school-going adolescents raises concern about the role of schools in this task. This study therefore assessed the role of schools in promoting positive oral health behaviour among adolescents through Capabilities, Opportunities, Motivation (COM-B) model in a Low-Income-Country.Methods Two thousand and ninety-seven students aged 12-18 years were recruited from 30 randomly selected Secondary Schools in a cross sectional study conducted in Ibadan, Nigeria. Data on Capabilities; Oral Health Knowledge (K), Attitude (A), Practices (P) and Motivation of the students as well as oral health promotional (OHP) activities (Opportunities) in the schools were assessed through a questionnaire. A checklist was used to assess availability of OHP materials and the schools’ tuck shops for sale of healthy food (Opportunities). Data were analyzed with STATA version 14.Results The mean KAP score was 43.8 (± 11.4)%. Oral health education was the only activity reported and this was in 8 (26.7%) schools; only 331 (15.8%) students had been educated about their oral health. There were no oral health promotional materials in the schools. About half 1161 (55.4%) were motivated to participate in school oral health program. All the tucks shops had cariogenic foods and drinks for sale. Students who had better KAP scores - Capabilities (OR = 1.2, 95%CI = 1.0-1.5, p = 0.018) or had been educated about oral health - Opportunities (OR = 1.5, 95%CI = 1.2-2.0, p < 0.001) were better motivated about their oral health.Conclusion The schools surveyed played very little or no role to support positive oral health behavior of adolescents. There were no OHP materials in the schools. Students who had superior oral health KAP (capabilities) or had been exposed to oral health education (opportunities) were better motivated about their oral health.