This is a pilot study evaluating the effectiveness, safety, and tolerability of Ritalin LA in treating Attention Deficit Hyperactivity Disorder (ADHD) in 4 and 5 year old children. Virtually no data has been published on the use of long-acting stimulant preparations in very young children despite early symptomatic development in a significant portion of young children with ADHD. This would be one of the first studies looking at a long-acting preparation of a stimulant medication in the treatment of ADHD in very young children.