There is concern that the risky behaviors of teenagers, such as truancy, negatively influence the behaviors of others through their social networks. We use administrative data to construct social networks based on students who are truant together. We simulate these networks to document that certain students systematically coordinate their absences. We validate them by showing that a parent information intervention on student absences has spillover effects from treated students onto their peers. Excluding these effects understates the intervention’s cost-effectiveness by 43%. We show that there is potential to use networks to target interventions more efficiently given a budget constraint.