PDF - http://www.ncjrs.org/pdffiles1/nij/210360.pdf
"'Juveniles often commit crimes in pairs or groups, a process known as co-offending. An NIJ-sponsored study of delinquents in Philadelphia found several patterns related to juvenile co-offending. The researchers linked co-offending with increased risks for recidivism and violence. Interaction among delinquent peers seems to instigate crimes and escalate their severity. The youngest offenders were more likely to co-offend and were more likely to become violent if their earliest crimes were committed with violent offenders, even if those crimes were not violent. The researchers recommend early intervention targeting very young offenders, especially co-offenders, although more research is needed. But, they also caution that some interventions may enhance the effects of co-offending by placing youths in groups that unintentionally provide negative peer learning.'"
