School-based drug prevention is a central component of drug control strategies. Evidence has repeatedly shown that some school-based drug prevention programs can produce statistically significant differences between treatment and control groups, and that those differences almost always decay by the end of high school. This study addressed the questions of whether these differences were significant, and which effects had the biggest impact on lifetime consumption and are most valuable in the long run. The data analyzed and social context considered were those of the United States. To estimate baseline drug consumption per person, the consumption per user was estimated, multiplied by the percentage of the population that ever uses, and adjusting for discounting. The results showed that the social benefits per participant stemming from reduced drug use ($840 from tobacco, alcohol, cocaine, and marijuana) appeared to exceed the economic costs of running the programs ($150 per participant). While the benefits associated with reduced cocaine use alone ($300) exceeded the costs, the corresponding figure for marijuana ($20) was small. Even if prevention reduced the use of other illicit drugs (such as heroin) by as much as it reduced use of cocaine, the majority of benefits would still stem from reductions in use of tobacco and alcohol, which has implications for how school-based drug prevention is funded and whether it is perceived more as a weapon in the war on illicit drugs or as a public health measure. Questions remain concerning the permanence of prevention’s effects and how to value instances of initiation being deferred but not completely prevented. 2 figures, 7 tables, 36 references