NRP104, Adderall XR or Placebo in Children Aged 6-12 Years With ADHD

Inclusion Criteria: * males and non-pregnant females, aged 6-12 years DSM-IV-TR criteria for diagnosis of ADHD, combined or hyperactive-impulsive subtypes * on stable regimen of stimulants for at least one month in the last six months and has shown adequate response to stimulants without unacceptable side effects Exclusion Criteria: * co-morbid psychiatric diagnosis such as psychosis, bipolar illness, severe OCD, severe depressive or anxiety disorder * history of seizure during the last 2 years, a tic disorder or Tourette's * clinically significant ECG or laboratory abnormalities at screening or baseline * taking clonidine or anticonvulsant drugs * taking medications that affect blood pressure or heart rate