4. to investigate the efficacy of MPH on the time perception measures among children and adolescents with ADHD; Subjects and Methods: This protocol consists of two studies. First, we will recruit 100 patients with DSM-IV ADHD, aged 9 to 16 years, and 100 school controls. They and their parents will receive K-SADS-E interviews. All of them will have complete assessments of time estimation, time discrimination, and time reproduction. Their parents also report on SNAP-IV and CPRS-R:S. The 2nd assessments will be performed 3 months later after the subjects received treatment at outpatients.