Developmental research on social influences on adolescents can guide practices aimed to prevent homicidal youth violence. School shootings have repeatedly raised questions about the contributory role of bullying and entertainment violence, how news media publicity might produce copycat crimes, and whether stiffer criminal sanctions might have a deterrent effect. This article presents the thoughts and recommendations of a group of experts on these topics summarizing the current knowledge base. In brief, bullying reduction programs may be a useful early prevention effort. Television and video games with violent themes can encourage aggressive behavior, but these media can be used to teach more prosocial behavior as well. The potential copycat effects of highly publicized crimes might be diminished with more restrained reporting, although more research is needed. Finally, there is substantial evidence that increased criminal sanctions for youthful offenders have not had a deterrent effect. (Contains 39 notes.)