The article first provides an overview of the nature of substantive due process and its application to school discipline. Both the U.S. Constitution and State constitutions guarantee that the government may not deprive any person of "life, liberty, or property without due process of law." Due process has two components: prosecutorial due process and substantive due process. Procedural due process essentially requires that when the state deprives a person of life, liberty, or property, the state must provide adequate procedural safeguards to protect against erroneous or unfair deprivations of constitutionally protected interests. Substantive due process, on the other hand, protects against arbitrary state action that deprives a person of life, liberty, or property. Students may not be excluded from school without due process. In Goss v. Lopez, (1975), the U.S. Supreme Court held that students have property and liberty interests in their education and that school districts must provide students with due process, even in the context of short-term suspensions. In order to address the question of whether possession of a weapon at school must be knowing in order to justify disciplinary exclusion from school, one section of the article discusses zero-tolerance polices related to weapon possession and assesses the court decisions in "Seal" and "Bundick," which differed in their rulings about whether possession of a weapon at school must be knowing in order to justify disciplinary exclusion from school. This assessment concludes that the Sixth Circuit Court's ruling in Seal v. Morgan was correct in holding that expelling a student for weapons possession, even if the student did not knowingly possess any weapon, violates substantive due process. The article argues that evidence of the student's knowing possession of a weapon is an important predicate for punishment, even in the context of school discipline. Without such evidence, severe punishment such as suspension does not have a rational basis. The "Seal" decision thus reflects the court's recognition of what is at stake for students who face expulsion under zero-tolerance policies. The article concludes with a discussion of some of the implications of the debate associated with zero-tolerance school policies, substantive due process, and weapons at school. 249 notes