Conservative estimates indicate there are at least 100,000 gang members in Los Angeles County alone. In the city of Los Angeles, the number of gangs increased from 450 in 1988 to 750 in 1991 and 1,000 in 1993. Gangs continually recruit new members, and most jailed gang members are eventually released back into their communities with more sophisticated contacts and knowledge. Gangs often emerge when businesses migrate out of the community, in areas where the job market has shifted from an industrial to a more service-oriented focus, and in areas where disorganization has been caused by rapid shifts in a community's ethnic makeup. Gang characteristics vary, depending on demographics, structure, degree of organization, and the social milieu in which they exist. The typical gang is divided into five or so small groups, each of which may have about 30 to 40 members. Gangs are overwhelmingly destructive in communities where they operate, with studies indicating gangs are associated with about 40 percent of all homicides. Gang activity and school violence are frequently related. Many believe strategies such as community and neighborhood mobilization and other social intervention techniques and opportunities must be employed to address the gang problem, and the school plays an important role in dealing with students at risk for gang involvement. 50 notes