Violence in school is not new. Especially on the college level, deaths and injuries from hazing have long occurred, as have student riots. However, widespread violence in public and secondary schools seems to have developed only in the past generation, especially in the United States, but also in other urban-industrial societies. One type of violence is perpetrated by predatory adolescent male trespassers who enter school buildings to steal or rob. This intruder violence is most common in the largest cities. The other major type of violence is committed by enrolled students against members of the school community: fellow students, staff members, and teachers. Both types of school violence can be understood in terms of the weakening of social control over adolescents and young adults in modern societies. Lack of family and neighborhood controls frees those youngsters not committed to the school and its values to express their predatory or aggressive impulses. Individual personality development also explains why some persons take advantage of these opportunities for violence offered in a fluid society. Alternative strategies for managing this problem are suggested. Tabular data, footnotes, and over 40 references are provided. (Author abstract modified)