The purpose of this study is to assess, in a controlled environment, the efficacy and safety of NRP104 and Adderall XR compared to placebo in treatment of children, aged 6-12, 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