Background: Poor access to and uptake of mental health interventions by adults and even adolescents has been highlighted in Nigeria and other low- and middle-income countries (LMICs). The literature indicates that less than 10% of Nigerians including the adolescent population access mental health intervention (Federal Ministry of Health (FMoH), 2013). The dearth of human and infrastructural resources among other resources have been highlighted as the predisposing factors to poor access. For instance, published findings have revealed that there are only eight psychiatric hospitals and 36 mental health units (in the general hospitals located across the 36 states of the country) that provide mental health interventions to over 214 million Nigerians (World Health Organisation, 2014b). This study was undertaken to develop a school based mental health programme (SBMHP) that will help to improve access to and uptake of mental health interventions by the adolescent population. Methods: A multiphase qualitative case study design was adopted to undertake this study. In Phase I, the researcher undertook a systematic literature review to identify the modules of SBMHPs that have been implemented in LMICs. A total of 11 articles were reviewed to elicit seven modules that were used as baseline data to guide phase II data collection. Phase II was done to generate culturally sensitive modules from participants drawn from diverse disciplines. 10 modules were generated from the 26 key informant interviews that were conducted. In Phase III, the researcher carried out triangulation of the findings from Phases II and III, to develop a hybrid programme. 10 modules were generated from this process. Phase IV involved the conduct of focus group discussions (FGD) with parents and teachers to confirm the applicability of the modules of the proposed hybrid programme and to subsequently modify the programme. A total of nine modules and three facilitators were generated from this Phase. 36 focus group discussants were involved in this Phase. Finally in Phase V, the researcher undertook member checking of the findings of the study to ensure rigour or trustworthiness of the study. The data were analysed using the five phases of analysis highlighted by Blanche et al. (2006). Results: The study findings were documented in four chapters. A total of seven modules, namely, an introduction module, a communication and relationship module, a psychoeducation module, a cognitive skills module, a behavioural skills module, a module on establishing social networks for recovery and help seeking behavioural activities, and a conclusion module were revealed from Phase I (Chapter Three). Five themes were generated from Phase II (Chapter Four). These themes were knowledge of mental health; adolescence and mental health; mental health institutions; access to mental health interventions; and the range of mental health interventions. In Chapter Five (Phase III), ten modules were reported as findings. The modules were as follows: introduction; life skills; social support; behavioural skills; mental health literacy; early diagnosis, treatment, and referral; creating and maintaining a healthy school environment; developing vocational skills; an overarching element and conclusion. Finally, nine modules and three facilitators were reported in Chapter Six (Phase IV). The modules include introduction; mental health literacy; life skills; behavioural skills; vocational skills; early diagnosis, treatment, and referral; social support; religious and traditional support; and conclusion. The facilitators included healthy environment; advocacy on resources (both human and capital); and training of teachers, parents, and other stakeholders. Other findings included the cultural sensitivity of the modules, recognising that spiritual and religious healers are part of the first line of contact, a concern with mental health problems in primary school children, and factors influencing the help seeking behaviour of parents and their children. Conclusion: This is the first study to generate culturally sensitive modules in LMICs. The findings of this study identified implications for policy development and deployment, the practice of child and adolescent mental health in schools and future studies. Some of the implications were as follows: advocacy for the inclusion of the contents of the developed school-based programme in the school curriculum; the development of some basic child and adolescent documents that will guide provision of mental health interventions in Plateau State; development of a protocol that can be used to provide mental health first aid in schools; and if applicable early identification and treatment. This study also produced a baseline programme that can be used to provide a myriad of interventions (mental health promotion, prevention, and early diagnosis and treatment) in schools in Plateau State, Nigeria and possibly other LMICs.