Long Acting Stimulant Treatment of Attention Deficit Hyperactivity Disorder (ADHD) in Young Children

Inclusion Criteria: * Informed consent obtained from the legal guardian. * Parent and child must be English-speaking. * The child must have been living with the parent or guardian for a minimum of 6 months at the time of study entry. * Age: 4-5 years of age at study entry. * weight of at least 15kg (20th percentile for 4 year olds) for boys and weight of at least 14.5kg (20th percentile for 4 year olds) for girls * Severity: age and sex-adjusted T score greater or equal to 65 on the Hyperactive- Impulsive Subscale of both the Conners Parent and Teacher Rating Scales (L) * Diagnosis: meets DSM-IV criteria for ADHD (hyperactive/impulsive or combined subtype), on Parent Diagnostic Interview Schedule for Children-IV (DISC-IV) and clinical interview by experienced clinician. ADHD must be the primary disorder. * Duration: symptoms must have been present for a minimum of nine months. * Impairment: less than or equal to 55 on the Child Global Assessment Scale. * Cognitive functioning: An estimated IQ 70 or greater on the Peabody Picture Vocabulary Test (PPVT). * School: participation in school-type program at least 2 half-days per week where class includes at least 8 peers; if child has been expelled from an eligible program in the 3 months before screening, they can be considered for enrollment as this may reflect severity of the disorder * Parents and patients must be able to attend regular study visits. * Children being treated with other stimulant or non-stimulant medications prior to enrollment will be allowed to discontinue treatment with these medications in order to enter the study, providing the parent wants to do so to enable their child to have a trial of Ritalin LA, the target symptoms are not well-controlled or unwanted side effects are persisting on their current treatment, and the prescribing physician is notified by the parent. These children will have a visit 1A in order to accommodate a 5 half-lives washout of their pre-study medication. Exclusion Criteria: * Other medications: no concurrent psychotropic medications or other medications (including herbal preparations and over-the-counter medications) with significant CNS effects (e.g., antidepressants, antipsychotics, drugs affecting blood pressure or heart rate, anticonvulsants, alpha-agonists, adrenergic blockers, lithium, or sedating antihistamines). * General medical conditions: children with major medical conditions that would interfere with involvement in the study or the study medication will not be enrolled. * Serious structural cardiac abnormalities: The recent joint advisory of the American Academy of Pediatrics (AAP) and the American Heart Association (AHA) recommend use of stimulant medications should generally be avoided in patients with cardiomyopathy, serious heart rhythm or structural abnormalities, or other serious cardiac problems. Any patient with such a diagnosis will not be allowed in this study. * Systolic and diastolic blood pressure above 95th percentile for age and gender * Exclusionary Psychiatric Conditions: Current Adjustment Disorder, Autism, Psychosis, Bipolar Disorder, PTSD, significant suicidality, or any other psychiatric disorder in addition to ADHD that requires treatment with additional medications. * History of physical, sexual, or emotional abuse that results in a clinically significant impact on clinical presentation, potentially driving some of the symptoms of ADHD. * Prior failure to respond to an adequate trial of any methylphenidate product. This will be at the determination of the investigator.