A Phase II, Adaptive Trial Design Examining the Pharmacokinetic and Pharmacodynamic Effects of Modified Release Amphetamine (HLD100, Formulations B, C and E)) in Adolescents and Children With Attention-Deficit Hyperactivity Disorder (ADHD)

Main Inclusion Criteria * Male and female adolescents (12-17 years; Stage 1) and children (6-11 years; Stage 2). * Diagnosis of ADHD and confirmed on Kiddie-Schedule for Affective Disorders and Schizophrenia (K-SADS). * ADHD symptoms controlled on a stable dose of Vyvanse, Adderall XR and or Dexedrine. * Provision of informed consent (from parent\[s\] or legal representative\[s\]) and assent (from subject) for patients. Main Exclusion Criteria * Comorbid psychiatric diagnosis (e.g., psychosis, bipolar disorder). * History of seizures or current diagnosis or family history of Tourette's disorder. * Use of prescription drugs (except Vyvanse, Dexedrine or Adderall XR) the 14 days and over-the-counter drugs (except birth control) the 30 days before the study.