In order to strengthen benefit-cost analyses of substance abuse prevention, this project will model the systemic costs of a large-scale National Institute on Drug Abuse-funded prevention effort known as PROSPER, estimate the societal value of targeting childhood substance risk factors, and identify best practices and research priorities for BCAs of prevention. By improving BCAs in this area, researchers can obtain more robust and reliable estimates that will facilitate more informed allocation of social resources and efficient substance abuse prevention efforts.