Multimodal Brain Imaging of Methylphenidate in Children and Adolescents With ADHD

Inclusion Criteria: * Age 6 to 18 years * Diagnosis of ADHD * A score of at least 3 (mildly ill) on the clinician administered Clinical Global Impressions-Severity (CGI-S) Exclusion Criteria: * Currently taking stimulant medications (within one week of first study visit). Patients will not be asked to discontinue any treatments for the purpose of this research study. Subjects will include treatment naïve patients and patients who were previously treated with stimulant medications, but are not currently treated, and meet study criteria. * Having an adverse reaction to methylphenidate, or other stimulant medication * Current psychiatric disorder, including bipolar I or II disorder, major depressive, disorder, obsessive-compulsive disorder, autism spectrum disorder, Tourette syndrome, or history of psychosis * Patient is at risk for clinically significant deterioration due to study protocol, as assessed by primary medical investigator (Dr. Grant) * Confirmed genetic disorder with cognitive and/or behavioral disturbances * Active, unstable medical illness that may interfere with cognition or compromises safety of the patient * History of head trauma with loss of consciousness or any evidence of functional impairment due to, and persisting after, head trauma * Neurological disorder, mental retardation, intellectual or disability, or other non-ADHD cause of cognitive impairment * Pregnant or breast-feeding women * Having a contraindication to MRI, including a pacemaker, defibrillator or other medical implant, other metal objects, or claustrophobia, or for having braces or other metal in the head region (likely to create an artifact on the MRI scans). * Currently smoking or using controlled or illicit substances, including alcohol.