Significance Despite a surge in policy and research attention to conflict and bullying among adolescents, there is little evidence to suggest that current interventions reduce school conflict. Using a large-scale field experiment, we show that it is possible to reduce conflict with a student-driven intervention. By encouraging a small set of students to take a public stance against typical forms of conflict at their school, our intervention reduced overall levels of conflict by an estimated 30%. Network analyses reveal that certain kinds of students (called “social referents”) have an outsized influence over social norms and behavior at the school. The study demonstrates the power of peer influence for changing climates of conflict, and suggests which students to involve in those efforts.

Abstract Theories of human behavior suggest that individuals attend to the behavior of certain people in their community to understand what is socially normative and adjust their own behavior in response. An experiment tested these theories by randomizing an anticonflict intervention across 56 schools with 24,191 students. After comprehensively measuring every school’s social network, randomly selected seed groups of 20–32 students from randomly selected schools were assigned to an intervention that encouraged their public stance against conflict at school. Compared with control schools, disciplinary reports of student conflict at treatment schools were reduced by 30% over 1 year. The effect was stronger when the seed group contained more “social referent” students who, as network measures reveal, attract more student attention. Network analyses of peer-to-peer influence show that social referents spread perceptions of conflict as less socially normative.

Footnotes Author contributions: E.L.P., H.S., and P.M.A. designed research; E.L.P. and H.S. performed research; P.M.A. contributed new reagents/analytic tools; E.L.P., H.S., and P.M.A. analyzed data; and E.L.P., H.S., and P.M.A. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

Data deposition: Replication codes are available at Dataverse (doi:10.7910/DVN/29199), and replication data are archived at Princeton University, with data available on request (subject to relevant Institutional Review Board consent).

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1514483113/-/DCSupplemental.