The mechanisms by which a whole-school intervention might improve sexual health: qualitative realist research nested in a trial in English secondary schools

Whole-school interventions go beyond classroom education, promoting health by modifying school environments. These can be effective in delaying sexual debut and increasing contraception use but mechanisms are poorly understood. Qualitative research within realist evaluation can explore mechanisms via building ‘context-mechanism-outcome configurations’, describing how interventions trigger mechanisms that interact with context to generate outcomes. We explored these for the Positive Choices whole-school sexual health intervention within the intervention arm of a randomised trial conducted 2021–2025. Using ‘dimensional analysis’, we analysed 52 interviews with teachers and 40 focus-groups involving 266 students from 22 English secondary schools. Our results suggest seven mechanisms through which whole-school interventions might ‘work’: improving knowledge using diverse pedagogies; improving confidence and ability to talk by normalising talk about sexual health; changing gender attitudes through challenging stereotypes and providing insights and empathy with others' perspectives; promoting access to sexual health and other services via helping students understand their needs and entitlements; building school engagement by providing new student roles on decision-making groups; increasing inclusion of sexual-minority students by normalising consideration of non-heterosexual identities and practices; and reducing sexual harassment and abuse by helping students understand consent and when to intervene in harassment. Contextual contingencies included: high initial student needs; teacher skills and commitment; and school commitment and capacity. Our research suggests novel mechanisms via which whole-school interventions might promote sexual health. Quantitative analyses will now be conducted to examine these mechanisms and contingencies.