The investigators recruited school bullying perpetrators from the age of 12 to 17 by referral from the local police department. An anti-bullying intervention based on cognitive-behavioral therapy (CBT) principles was conducted, and addressed issues related to impulse control, empathy and communication enhancement. All participants completed brain magnetic resonance imaging, neurocognitive tests, and questionnaires before and after the intervention.

The present study included previous perpetrators of school bullying who were convicted for a minor offense, including physical or verbal assaults or theft, and who were referred by the police to participate in an anti-bullying intervention. The program consisted of 8 sessions over 4 weeks and was conducted by a board-certified psychiatrist and a therapist with previous training in psychosocial treatments. The intervention was based on CBT principles and addressed various factors that have been associated with perpetrators of school bullying, including impulse control, perspective taking (empathy), and the enhancement of communication skills.

All participants completed the Korean Kiddie Schedule for Affective Disorders and Schizophrenia-Present and Lifetime version (K-SADS-PL) administered by board-certified child and adolescent psychiatrists. The validity and reliability of the original and Korean versions of the K-SADS-PL have been established. Intelligence quotient (IQ) was measured using the Korean Educational Developmental Institute's Wechsler Intelligence Scale for Children.

Prior to and after participation in the program, all participants underwent brain magnetic resonance imaging (structural and functional) and completed neurocognitive tests that included the continuous performance test (CPT), the Stroop Word and Color Test, and the Wisconsin Card Sorting Test (WCST). The parents of the participants completed questionnaires including the Child Behavior Checklist (CBCL). Written informed consent was obtained from the parents and the participants after sufficient explanation of the study. The study protocol was approved by the institutional review board of the Seoul National University Hospital.

Inclusion Criteria:

• No psychiatric diagnosis or psychiatric diagnoses including conduct disorder, depressive disorder, oppositional defiant disorder, attention-deficit hyperactivity disorder, and adjustment disorder.
• IQ > 70
• Agreement to participate
• Ability to cooperate in group therapy

Exclusion Criteria:

• Any psychotic disorder
• Severe impairment in impulse control
• Not cooperating with program participation
• IQ < 70
• Current or past history of brain trauma or organic brain disorder, seizure disorder, or any neurological disorder.