Background: The traditional focus of adolescent sexual health research is on risk and adverse outcomes and on first vaginal intercourse as a portent of risk. This preoccupation with first sex limits research on social processes of sexual development and is out of step with the contemporary reality of young people’s early sexual experiences in which vaginal sex (if it happens at all) often follows a wide range of intimate and sexual experiences. Aim: With an innovative approach combining latent class analysis and social network analysis, we assessed how sexual knowledge, positive norm adherence, confidence and sexual activity are patterned across school-year social networks and explored the extent to which individualist and social influence theories could explain these patterns. Methods: We analysed cross-sectional survey data from 10 school year-group (students age 14-16) from the STis And Sexual Health (STASH) feasibility study. Students completed measures on sexual health knowledge, norms, confidence and behaviours, and named up to six friends in their year group. We used Latent Class Analysis to categorise patterns of sexual behaviour, and Exponential Random Graph Models to assess how sexual behaviour, knowledge, norms and confidence related to friendship ties. Results: Of 1,446 students 21% (n=309) did not report any sexual experience (inactive), 42% (602) reported some sexual experience but not oral or vaginal sex, and 22% (323) had oral and/or vaginal sex. Friendship ties were more likely between students who had similar levels of competencies (knowledge, norms and confidence). Friendships were also more likely between students who were sexually inactive (OR 1.73 95% CI 1.54, 1.95), and between students who reported oral/vaginal sex (OR 1.77 95% CI 1.46, 2.15). Active but not oral/vaginal sex students were slightly less likely (OR 0.86 95% CI 0.75, 0.99) to have friendship ties with each other. Interpretation: Our findings suggest that peer influence operating on sexual health competencies may occur independently of current sexual behaviour and there may not be strong naturally occurring social influence process to initiate pre-intercourse sexual behaviours. Our findings suggest that sexual health interventions acting on network influences are justified and that the focus of such interventions should shift from first intercourse to patterning of developing sexual repertoires.