Estimates the amount of social benefit that prevention programs generate through reductions in the use of cocaine, marijuana, alcohol, and tobacco; Unlike drug enforcement, school-based prevention programs reduce the use of licit substances, as well as illicit ones. The authors examine which substances are principally responsible for prevention's benefits by estimating how much benefit is generated from reduced use of cocaine, marijuana, alcohol, and tobacco. They find that the benefits of prevention programs outweigh their costs, with alcohol and tobacco accounting for about two-thirds of prevention's drug-use reduction benefits.