This is a prospective (study following participants forward in time), single-arm, open-label (all people know the identity of the intervention), 8-week, multi-centric (conducted in more than 1 center) study. OROS-MPH will be administered orally for 2 months at doses of 18, 36, or 54 milligram (mg) to replace IR-MPH. Clinicians will adjust the dose of each participant according to participant's clinical responses and/or side effects. During the study period, participants will be assessed on Week 2, 4, and 8. Efficacy will be evaluated primarily based on change from baseline in Chinese version of the 26-item Swanson, Nolan and Pelham-Fourth Edition (SNAP-IV) rating scale assessed by parents and Chinese Health Questionnaire (CHQ). Safety will be monitored throughout the study.