Philosophiae Doctor - PhD / This study focused on developing an intervention programme for school health nurses on guiding adolescents in their decision-making on reproductive health. A review of literature shows that this role is necessary, as there is a great need to reduce adolescents' morbidity and mortality rates due to poor decision-making about their reproductive health. School health nurses are strategically positioned to perform this role in ensuring that adolescents are well guided in making responsible decisions about their reproductive health. However, available evidence shows that school health nurses have not been performing this role in the school health service, especially in Nigeria. The provision of guidance for adolescents, on making decisions about their reproductive health is an adaptive role of school health nurses. The literature further shows that school health nurses require adequate preparation before they can perform this role. The study was conducted in the secondary school environment of Ijebu Ode local government area of Nigeria. Work role performance theory, adult learning principles, and experiential learning constituted the theoretical point of departure for this study. The paradigmatic assumptions revolved around intrepretivism/constructionism using the qualitative methodological approach. Semi-structured interviews and focus groups were the means of obtaining information from study participants for the study. The Intervention Design and Development model of Rothman and Thomas (2013) was used to design the study. The participants for the study were eight school health nurses, five school teachers, thirty-six adolescents, and one school health coordinator. They were all purposively selected. The data collected was analysed manually using inductive content analysis. The main findings from the interviews show that school health nurses have a poor awareness of their role and responsibilities, a lack of knowledge on how adolescents make their decisions, a lack of adequate knowledge on how to guide adolescents in their decision-making. The findings also show that there is poor interpersonal communication between school health nurses, and adolescents, and between school health nurses and members of the teaching staff. The findings further show that there are insufficient continuous professional development programmes. Results from integrative reviews regarding the types of intervention programmes that had been developed for school health nurses at different times in the past focused on role orientation, knowledge and skills acquisition, and mutual interaction between school health nurses and adolescents, and members of the teaching staff. The findings reflect a gap in how school health nurses provide guidance to school adolescents in decision-making on their reproductive health, hence the need for a training programme that will assist them in discharging this function effectively. A training programme was designed and developed for school health nurses to assist them on guiding adolescents in their decision making about their reproductive health. The training programme was pilot tested with observational methods, an interview being used as a means of assessing the quality and outcomes of the training programme. The results of the pilot test show the participants' satisfaction with the organisation and the quality of the training workshop. Participants indicated that they had gained more knowledge and understanding of adolescent reproductive issues, and their decision-making processes. They also said that they had gained more interpersonal skills, and greater communication skills. Some expressed the conviction that they had gained more confidence in their ability to communicate with the teaching staff. Some also expressed their readiness to apply the skills obtained during the training to their practice area. It is recommended that the training programme be fully evaluated in phase five of the Intervention Design and Development model of Rothman and Thomas, which will enable full dissemination and implementation of the programme (Rothman and Thomas, 2013). It is further recommended that the training programme be disseminated to end users (school health nurses) by sensitizing the necessary stake-holders on the need to use the training programme for school health nurses in their respective school contexts.