This study examined the impact on high school students who taught elementary students MADD's Protecting You/Protecting Me (PY/PM), an alcohol use prevention and vehicle safety program. High school students ( N = 188) enrolled in a peer helping course completed surveys before and after teaching PY/PM, and a comparison group of peer helper students ( N = 141) from matched schools completed surveys at the same times. Results indicated that, relative to the comparison group, those exposed to PY/PM gained knowledge of alcohol's effects, increased their perceptions of the risks of high levels of alcohol use, gained teaching skills, and showed less frequent episodes of binge drinking. No effects were found for attitudes toward future drinking, perceptions of the risk of low levels of alcohol use, alcohol use, or vehicle safety. This cross-age prevention program may be successful in changing high school students' knowledge, attitudes, and behaviors regarding high levels, but not low levels, of alcohol use.