The Multiple-Family Group Intervention (MFGI) was developed to address the need for an effective and yet affordable treatment for reducing recidivism for incarcerated adolescents and altering the families’ coercive interactional patterns from an affect regulation and attachment perspective. The 8-week MFGI program was conducted in two Indiana juvenile correctional institutions. The research study utilized pre- and postintervention assessments and a 6-month follow-up assessment. Data from both male (n = 43) and female (n = 30) adolescents were combined, yielding a total sample of 140 respondents (73 adolescents, 67 caretakers). The 6-month follow-up assessment indicated a recidivism rate of only 44% compared to the national norm of 65–85%. Linear growth models were fit to determine the nature of the changes in adolescent behavior over the three assessments. Adolescents and caregivers reported that adolescents’ externalizing behaviors significantly declined over time. Adolescent-reported internalizing symptoms as well as their alcohol and drug use significantly declined over the follow-up period, while caregiver reports of these behaviors showed no change over time. Adolescent-reported attachment to their parents, particularly mothers, increased significantly as did both adolescent and caregiver-reported functional affect regulation.