The primary objective of this study is to assess the time of onset of Vyvanse compared to placebo, in the analog classroom as measured by the Swanson, Kotkin, Agler, M. Flynn and Pelham (SKAMP) deportment scale in children (aged 6-12) diagnosed with Attention-Deficit/Hyperactivity Disorder (ADHD).

Inclusion Criteria:

1. Subject is a male or female aged 6-12 years inclusive at the time of consent.
2. Females of Child-bearing Potential (FOCP) must have a negative serum beta Human Chorionic Gonadotropin (HCG) pregnancy test at Screening and a negative urine pregnancy test at Baseline and agree to comply with any applicable contraceptive requirements of the protocol.
3. Primary diagnosis of ADHD: combined sub-type or predominantly hyperactive impulsive sub-type based on a detailed psychiatric evaluation.
4. Subject has a baseline ADHD-RS-IV score ≥ 28.
5. Intelligent Quotient (IQ) score of 80 or above on the Kaufman Brief Intelligence Test (KBIT).
6. Subject must be able to complete at least the Basic Test of the PERMP assessment.

Exclusion Criteria:

1. Subject has a current, controlled (requiring a restricted medication) or uncontrolled, comorbid psychiatric diagnosis with significant symptoms such as Post Traumatic Stress Disorder (PTSD), psychosis, bipolar illness, pervasive developmental disorder, severe obsessive compulsive disorder, severe depressive or severe anxiety disorder
2. Subject has Conduct Disorder.
3. Subject has a documented allergy, hypersensitivity or intolerance to amphetamines.
4. Subject has failed to respond to one or more adequate courses (dose and duration) of amphetamine therapy.
5. The subject has a recent history (within the past 6 months) of suspected substance abuse or dependence disorder (excluding nicotine) in accordance with DSM-IV-TR criteria.
6. Subject weighs less than 50 pounds (22.7kg).
7. Subject is significantly overweight
8. Subject had a history of seizures during the last two years (exclusive of febrile seizures), a tic disorder, a current diagnosis and/or family history of Tourette's Disorder.
9. Subject has any reported history of abnormal thyroid function.
10. Subject has taken another investigational drug or taken part in a clinical trial within the last 30 days prior to Screening.
11. Subject has a known history of structural cardiac abnormality, as well as any other condition(s) that may affect cardiac performance.
12. Subject has a concurrent chronic or acute illness (such as severe allergic rhinitis or an infectious process requiring antibiotics), disability, or other condition that might confound the results of safety assessments
13. Subject is taking other medications that have central nervous system (CNS) effects or affect performance, such as sedating antihistamines and decongestant sympathomimetics (bronchodilators are not exclusionary).
14. The female subject is pregnant or lactating.
15. Subject is well controlled on their current ADHD medication with acceptable tolerability.