 This study evaluates how children with Attention Deficit Disorder without Hyperactivity ADD respond to medication, and if their response is different from children who have problems with both hyperactivity and inattention. In order to do this, children ages 7-11 whose primary difficulty is with attention problems and who have never been on behavioral or psychiatric medications are being recruited. Once enrolled, children will try one week each of 3 different doses of methylphenidate, the most commonly prescribed Attention Deficit, Hyperactivity Disorder ADHD medication, as well as placebo. Children will be randomly assigned to one of six possible medication dose and placebo titration schedules, but the study doctor, family, and teacher will not know which dose if any children are receiving for a given week. Each week, behavioral and side effect ratings will be completed by both the childs parent and teacher, and the family will meet with the study doctor for a physical examination and to discuss how each week went. Some children will also have neuropsychological testing to determine how methylphenidate influences their working memory, sustained attention, and ability to inhibit stop inappropriate responses. 