This randomized, double-blind, flexible-dose, placebo-controlled, parallel group study is designed to evaluate Aptensio XR® compared to placebo in preschool age children with ADHD. Male and female children ages 4 years, 0 months to 5 years, 8 months with a diagnosis of ADHD (combined, inattentive or hyperactive/impulsive presentation) based on the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) criteria will be enrolled. Diagnosis will be determined using the Kiddie-Sads-Present and Lifetime Version (K-SADS-PL), which has been used in this age group.11 ADHD-RS IV ratings obtained at screening will include the 6-months immediately prior to screening.