The testing procedure is as follows: (1) All children (ADHD group and normal controls) will be assessed IQ and a series of neuropsychological assessments. Their parents will complete the SNAP-IV scale at the same time. (2) After that, children with ADHD will take IR MPH (at the same dose as their prescription) and rest for approximately 45 minutes. Meanwhile, parents of children with ADHD will be interviewed with K-SADS-E by trained interviewer. (3) Children with ADHD will then be re-assessed CPT. CGI and Behavior observation will be assessed.