This is a single site, open-label, four-week feasibility study of long-duration beaded methylphenidate (B-MPH), also known as Ritalin LA™. B-MPH is a FDA-approved medication for children 6 years and older with attention-deficit/hyperactivity disorder (ADHD), but there are no studies of its use in preschoolers. This study will evaluate the safety and effectiveness of B-MPH for ADHD treatment in 4-to-5-year old children.