Most delinquent behavior occurs within age-homogeneous peer groups. Using incident-level data from the National Incident-Based Reporting System (NIBRS), this study reassesses the extent to which contemporary juvenile group offending reflects peer-only networks versus cross-age collaboration. Results show that while juvenile-only groups remain the dominant pattern, approximately one-third of co-offending incidents involve adult participants. Mixed-age groups are associated with group size, offense type, and situational context, and are especially common in serious offenses such as homicide, aggravated assault, and drug crimes. Mixed-age co-offending is also associated with greater offense severity, particularly higher odds of victim physical injury. These findings have important implications for the criminal justice system’s response to juvenile crime. While most juvenile offending diversion programs currently focus on interventions that counter peer influence and reduce the time spent with peers engaging in antisocial behavior, intervention strategies that also address the facilitating role of adult co-offenders may also be necessary.
