Symptoms resulting from childhood trauma can negatively impact socioemotional well-being and school performance during early adolescence unless positive changes in attachment security and mental representations of significant relationships occur. A sample of 109 eighth grade urban students were randomly assigned to one of two weekly, one-hour, school-based group interventions—Storytelling/Story-Acting for Adolescents (STSA-A) or Mentalization-Based Treatment Group Intervention (MBT-G). The Object Relations Inventory (ORI), Adolescent Attachment Questionnaire (AAQ) and Child PSTD Stress Scale (CPSS) were administered to students and their primary group leaders at the beginning (October) and end (May) of the intervention protocol as outcome variables. Participants in both the STSA-A and MBT-G intervention conditions experienced significant increases in attachment security and decreases in trauma symptoms. Over the course of eight months of group intervention, affective valence of paternal mental representations significantly decreased for boys and for participants in the STSA-A condition, while affective valence of primary group leader mental representations significantly decreased for participants in the MBT-G condition. STSA-A and MBT-G were found to be efficacious at improving attachment security and reducing trauma symptoms in young adolescents. The strengths of each group intervention for addressing interpersonal issues unique to specific types of adolescents are discussed.