IntroductionChildren’s learning abilities suffer when their oral health is compromised. Inadequate oral health can harm children’s quality of life, academic performance, and future success and achievements. Oral health problems may result in appetite loss, depression, increased inattentiveness, and distractibility from play and schoolwork, all of which can lower self-esteem and contribute to academic failure. An oral health curriculum, in addition to the standard school curriculum, may instil preventive oral hygiene behaviour in school students, enabling them to retain good oral health for the rest of their lives. Because most children attend school, the school setting is the most effective for promoting behavioural change in children. A ‘health-promoting school’ actively promotes health by enhancing its ability to serve as a healthy place to live, learn and work, bringing health and education together. Making every school a health-promoting school is one of the joint objectives of the WHO and UNICEF. The primary objective of this proposed study is to assess the effectiveness of an oral health curriculum intervention in reducing dental caries incidence and improving oral hygiene behaviour among high school children in grades 8–10 of the Ernakulam district in Kerala, India. If found to be effective in changing children’s behaviour in a positive way, an oral health curriculum may eventually be incorporated into the school health curriculum in the future. Classroom interventions can serve as a cost-effective tool to increase children’s oral health awareness.Methods and analysisThis protocol presents a cluster randomised trial design. It is a parallel-group comparative trial with two arms having a 1:1 distribution—groups A and B with oral health curriculum intervention from a dental professional and a schoolteacher, respectively. High schools (grades 8–10) will be selected as clusters for the trial. The minimum cluster size is 20 students per school. The total sample size is 2000 high school children. Data will be collected at three time points, including baseline, after 1 year (mid-term) and 2 years (final), respectively. The outcome measures are Decayed, Missing and Filled Teeth Index; Oral Hygiene Index-Simplified; and knowledge, attitude and behaviour. Data collection will be done by clinical oral examination and questionnaire involving oral health-related knowledge, attitude and behaviour items.Ethics and disseminationEthical approval was obtained from the Institutional Ethics Committee of Amrita Institute of Medical Sciences and Research Centre (dated 19 July 2022, no: IEC-AIMS-2022-ASD-179).Trial registration numberClinical Trial Registry of India (CTRI/2022/09/045410).