Evaluate Safety and Efficacy of ORADUR®-Methylphenidate in Children and Adolescents With ADHD

Main inclusion criteria: 1. Female or male subjects with age between 6 and 18 years old. 2. Subjects with documented diagnosis of one of the three presentations of Attention Deficit Hyperactivity Disorder (ADHD) within one year by investigator assessment using Diagnostic \& Statistical Manual for Mental Disorders-Fifth Edition (DSM-5). 3. Both subjects and parents/guardians have provided their signed and dated informed consent form for the study. Main exclusion criteria: 1. Subjects have received ADHD treatment for over 1 year or those who have received other ADHD treatment within 30 days prior to the study treatment initiation. 2. By investigator's evaluation, subjects are very anxious, tense or agitated. 3. Subjects known to be allergic to any ORADUR®-methylphenidate ingredients. 4. Subjects with an estimated intelligence quotient (IQ) \< 80. 5. Subjects are taking a concomitant medication (ex: Monoamine Oxidase Inhibitor (MAOI)) that is likely to interfere with safe administration of methylphenidate within 14 day prior to the study treatment initiation. 6. Subjects are joining other clinical studies and receiving any other investigational medical products within 30 days prior to the study treatment initiation. 7. Subjects have glaucoma (narrow angle glaucoma), on-going seizure disorder, or other psychotic disorder. 8. Subjects have chronic tics, Tourette's syndrome, or a family history of Tourette's syndrome. 9. Subjects have clinically significant gastrointestinal problems, including narrowing of the gastrointestinal tract. 10. Subjects/caregivers are (in the case of subjects whose parents/caregivers were to fill out the study questionnaires) with drug or alcohol abuse/dependence within the prior 6 months. 11. By the investigators' discretion, subjects with serious or unstable medical illness that will interfere with the evaluations of study efficacy and safety. 12. In the investigators' opinion, subjects cannot understand or follow the instructions given in the study. 13. Psychological, familial, sociological, or geographical condition potentially hampering compliance with the study protocol and follow-up schedule.