The World Health Organisation, amongst others, recognises that adolescent men have a vital yet neglected role in reducing teenage pregnancies and that there is a pressing need for educational interventions designed especially for them. This study seeks to fill this gap by determining the feasibility of conducting an effectiveness trial of the If I Were Jack intervention in post-primary schools. This 4-week intervention aims to increase teenagers’ intentions to avoid unintended pregnancy and addresses gender inequalities in sex education by explicitly focusing on young men. A cluster randomised feasibility trial with embedded process evaluation will determine: recruitment, participation and retention rates; quality of implementation; acceptability and feasibility of the intervention and trial procedures; and costs.