The nature of student violence in America's schools has changed over the past two decades. Research suggests that there are two distinct kinds or "subtypes" of aggression in youth-reactive aggression and proactive aggression. Reactive aggression is characterized as a "hot-blooded," automatic, defensive response to immediate and often misperceived threat. Proactive aggression, on the other hand, is described as highly organized, "cold-blooded," and premeditated rather than automatic. According to responses from a national survey of school administrators, the frequency of proactive aggression has doubled among middle and high school students and nearly tripled at the elementary school level in the past 20 years. The purpose of this article is twofold: (a) to report findings of an inquiry into the impact of increasing proactive aggression in schools as experienced by principals and assistant principals nationwide, and (b) to present the views of "front line" school leaders with regard to the impact, causes and potential solutions to the problem. (Contains 2 tables.)