Background: Internalizing and externalizing behaviors often emerge during adolescence. Early interventions could prevent severe or chronic mental health issues such as depression, suicidal tendencies, crime, and social harm, thereby potentially mitigating their adverse consequences. Objectives: The present study aimed to investigate the effects of schema therapy for children and adolescents (ST-CA) on the externalizing behaviors of the adolescents referred to the counseling centers in Ahvaz, Iran. Methods: This quasi-experimental study was conducted with a pretest-posttest design and a control group. The sample population included adolescents aged 12 - 14 years with behavioral, educational, and mood problems who were referred to the counseling centers in Ahvaz, Iran in 2020. In total, 30 adolescents were selected via convenience sampling and randomly divided into two groups of experimental and control (15 per each). The experimental group received 14 sessions of ST-CA (120-minute weekly sessions). Data were collected using the child behavior checklist. Data analysis was performed in SPSS version 26.0. Results: In the experimental group, the mean scores of externalizing behaviors at the pretest and posttest were 70.52 ± 6.11 and 58.27 ± 4.80, respectively. The mean score of aggression in the experimental and control groups at the posttest was 57.60 ± 3.83 and 64.20 ± 7.41, respectively. The mean score of rule-breaking in the experimental and control groups at the posttest was 55.53 ± 6.10 and 61.07 ± 7.63, respectively. ST-CA could significantly alleviate the externalizing behaviors of the subjects, such as aggression and rule-breaking (P < 0.001). Conclusions: According to the results, ST-CA could effectively decrease externalizing behaviors. Therefore, this approach should be incorporated into the interventions designed for these cases. Our findings could lay the groundwork for further investigation in this regard.