Background: Attention deficit hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders in school-aged children. Objectives: This study assessed the effectiveness of metacognitive therapy in behavioral-emotional problems, cognitive-emotional regulation strategies, and mind wandering in children with ADHD. Methods: This quasi-experimental study utilized a pretest-posttest design with a control group. The statistical population comprised all students referred to the West Health Center of Ahvaz in 2019. A sample of 45 patients was selected and randomly divided into intervention (MCT, n = 15) and control (n = 15) groups. The experimental group underwent eight sessions (90-minute sessions per week) of MCT, and the control group did not receive any intervention. The research instruments included the Cognitive-Emotional Regulation Questionnaire-children form (CERQ-K-P), Rutter Children Behavior Questionnaire (RCBQ), and Mind Wandering Questionnaire (MWQ). Multivariate analysis of covariance was used to analyze the data. Results: The participants included 30 children aged 10.92 ± 2.02 years. In the experimental group, the average score of behavioral-emotional disorder changed from 30.78 to 24.14, cognitive-emotional regulation strategies from 58.34 to 69.43, and mental wandering from 78.18 to 85.14. In the control group, the average score of RCBQ changed from 29.17 to 30.58, CERQ-K-P from 54.5 to 52.34, and MWQ from 19.77 to 19.87. The MCT effectively reduced behavior-emotional problems and mind wandering and improved cognitive-emotional regulation strategies in children with ADHD (P < 0.05). Conclusions: Metacognitive therapy improved behavioral-emotional problems, cognitive-emotional regulation strategies, and mind wandering in ADHD children. Therefore, metacognitive and psychiatric treatments are recommended for these patients.