A Trial of Centanafadine Efficacy and Safety in Children With Attention-deficit/ Hyperactivity Disorder (ADHD)

Inclusion Criteria: * Males and females aged 4 to 12 years (inclusive) at the time of informed consent/assent. * A primary diagnosis of ADHD based on Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) diagnosis criteria as confirmed with the Mini International Neuropsychiatric Interview for Children and Adolescents (MINI-KID). * A minimum symptoms total raw score of ≥ 28 on the ADHD-RS-5 at baseline for all subjects. * A score of 4 or higher on the CGI-S-ADHD at baseline. * Subjects aged 4 or 5 years only: has failed adequate psychotherapy or in the investigator's opinion, is severe enough to require pharmacotherapy in the absence of prior psychotherapy. Exclusion Criteria: * Comorbid diagnosis of: Tourette's Disorder, Generalized Anxiety Disorder that is severe enough to interfere with trial procedures, Panic Disorder, Conduct Disorder, Psychosis, Post-traumatic Stress Disorder, Bipolar Disorder, Autism Spectrum Disorder, Oppositional Defiant Disorder that is severe enough to interfere with trial conduct (allowed if it is not the primary focus of treatment), Obsessive-Compulsive Disorder that is severe enough to interfere with trial conduct (allowed if it is not the primary focus of treatment), or major depressive disorder (MDD) with current major depressive episode. * A significant risk of committing suicide based on history and the investigator's clinical judgment, or routine psychiatric status examination, Current suicidal behavior, Imminent risk of injury to self, Active suicidal ideation. A history of suicidal behavior (over the last 6 months). * Body mass index (BMI) ≥ 40 kg/m2 or ≤ 5th percentile for age and gender based on US Centers for Disease Control and Prevention (CDC) criteria. * Has initiated, changed, or discontinued receiving psychological interventions for ADHD within the 30 days before the screening visit, or is anticipated to start new treatment during the trial.