Background <p>COVID-19 containment measures have led to an increase in emotional and behavioral problems (EBP) in children. Studies show positive effects of interventions with teacher training in reducing EBP in children. </p> Objective <p>This study aimed to implement and verify the effects of an online ABA-based teacher training program on prosocial behaviors and EBP in students returning to in-person classes during the COVID-19 pandemic.</p> Methods <p>Participants included 345 parents/caregivers of 2nd and 3rd grade elementary school students and their 37 teachers, divided into a control group (CG) and an intervention group (IG). Teachers in the IG received online ABA-based training focused on EBP and prosocial behaviors contents, while those in the CG were exposed to reading strategies contents. The Strengths and Difficulties Questionnaire (SDQ) (parents and teachers), sociodemographic and socioeconomic questionnaires, and checklists to monitor strategies used by teachers were used. </p> Results <p>The results showed that parents in the IG perceived a decrease in EBP, with statistically significant results in conduct problems (p=0.046) and hyperactivity (p=0.039), while teachers perceived a reduction in hyperactivity (p=0.007) and emotional problems (p=0.043) in the post-intervention (Time 2). The greater the use of ABA-based strategies by teachers, the lower the occurrence of EBPs among students (r=-0.31). No significant reductions in EBP were observed in the CG.</p> Conclusion <p>These results indicate that online ABA-based teacher training is a low-cost intervention that has produced positive effects in promoting students' mental health, including reducing EBP and improving students' prosocial behavior.</p>