Despite the controversies that it has created in school districts throughout the country, zero tolerance continues to be a widely used response to school disruption and violence. This paper explores the history, philosophy, and effectiveness of zero-tolerance school disciplinary strategies. Growing out of Reagan-Bush-era drug-enforcement policy, zero-tolerance discipline attempts to send a message by punishing both major and minor incidents severely. Analysis of a representative range of zero-tolerance suspensions and expulsions suggests that controversial applications of the policy are not idiosyncratic, but may be inherent in zero-tolerance philosophy. There is as yet little evidence that the strategies typically associated with zero tolerance contribute to improved student behavior or overall school safety. Research on the effectiveness of school-security measures is extremely sparse, while data on suspension and expulsion raise serious concerns about both the equity and effectiveness of school exclusion as an educational intervention. Community reaction has led some districts to adopt alternatives to zero tolerance, stressing a graduated system matching offenses and consequences, and preventive strategies, including bullying prevention, early identification, and improved classroom management. Building a research base on these alternatives is critical to assist schools in developing more effective, less intrusive methods for school discipline. (Contains 101 references.) (Author/WFA)