Background:Dating and relationship violence (DRV)-intimate partner violence during adolescence-encompasses physical, sexual and emotional abuse. DRV is associated with a range of adverse health outcomes including injuries, sexually transmitted infections, adolescent pregnancy and mental health issues. Experiencing DRV also predicts both victimisation and perpetration of partner violence in adulthood.Prevention targeting early adolescence is important because this is when dating behaviours begin, behavioural norms become established and DRV starts to manifest. Despite high rates of DRV victimisation in England, from 22 to 48% among girls and 12 to 27% among boys ages 14-17 who report intimate relationships, no RCTs of DRV prevention programmes have taken place in the UK. Informed by two school-based interventions that have shown promising results in RCTs in the USA-Safe Dates and Shifting Boundaries-Project Respect aims to optimise and pilot a DRV prevention programme for secondary schools in England. Methods:Design: optimisation and pilot cluster RCT. Trial will include a process evaluation and assess the feasibility of conducting a phase III RCT with embedded economic evaluation. Cognitive interviewing will inform survey development.Participants: optimisation involves four schools and pilot RCT involves six (four intervention, two control). All are secondary schools in England. Baseline surveys conducted with students in years 8 and 9 (ages 12-14). Follow-up surveys conducted with the same cohort, 16 months post-baseline. Optimisation sessions to inform intervention and research methods will involve consultations with stakeholders, including young people.Intervention: school staff training, including guidance on reviewing school policies and addressing 'hotspots' for DRV and gender-based harassment; information for parents; informing students of a help-seeking app; and a classroom curriculum for students in years 9 and 10, including a student-led campaign.Primary outcome: the primary outcome of the pilot RCT will be whether progression to a phase III RCT is justified. Testing within the pilot will also determine which of two existing scales is optimal for assessing DRV victimisation and perpetration in a phase III RCT. Discussion:This will be the first RCT of an intervention to prevent DRV in the UK. If findings indicate feasibility and acceptability, we will undertake planning for a phase III RCT of effectiveness. Trial registration:ISRCTN, ISRCTN 65324176. Registered 8 June 2017.