Study of Atomoxetine and OROS Methylphenidate to Treat Children and Adolescents Ages 6-17 With ADHD

Inclusion Criteria: * Male and female outpatients from 6 to 17 years old. * Subjects with a DSM-IV diagnosis of ADHD by clinical interview, confirmed by the KSADS-E ADHD module. * Subject with DSM-IV diagnosis of ADHD without previous treatment. * Subjects with DSM-IV diagnosis of ADHD with a clinical history of a partial response to ATMX or methylphenidate as monotherapy. * In phase I, subjects with a CGI-Severity of at least moderate impairment related to their ADHD (CGI \>4). * In phase II, subjects receiving therapeutic doses of ATMX with at least minor improvement in their clinical picture due to the ATMX as determined operationally (CGI-Improvement score indicating at least minor improvement relative to off-drug baseline) will be included. * In phase II, only subjects receiving ATMX that also have evidence of persistent symptoms of ADHD and impairment related to their ADHD (a CGI-Severity of \> minor impairment OR ADHD RS \>18; AND GAF score \<65) will have Concerta added to their regimen. * Subjects' parents must provide informed consent and subjects' assent. Exclusion Criteria: * Pregnant or nursing females or females not using proper contraception. * Subjects with a medical condition or treatment that will either jeopardize subject safety or affect the scientific merit of the study. * Subjects (or their families) who do not appear to be reliable reporters of their condition or who indicate they will not be able to meet the schedule of visits for the duration of the study. * Subjects with Mental Retardation or Organic Brain Syndromes. * Subjects who have a lifetime history of a psychotic or bipolar disorder. * Subjects with recent or current (past 30 days) major depressive disorder or a clinically significant anxiety disorder that would potentially necessitate treatment during the trial. g. Subjects with recent evidence (past 30 days) of suicidality or homicidality will not be enrolled. * Subjects with a recent history (e.g. three months) of a substance use disorder; or those with a positive urine for substances of abuse will not be enrolled. Subjects will be told that a positive urine for substances of abuse will be disclosed to their parents. * Subjects taking stimulants or other psychotropics at the time of the evaluation. Subjects will not be discontinued from their current medication regimen (not including ATMX), unless authorized and supervised by their treating physician. * Treatment of stimulants within one week of the evaluation; tricyclic antidepressants, bupropion, cholinesterase inhibitors, modafinil, clonidine/guanfacine, lithium/anticonvulsants for behavioral control, or serotonin reuptake inhibitors (except fluoxetine) for four weeks prior to entry are prohibited. Treatment with antipsychotics/neuroleptics and fluoxetine for 8 weeks prior to entry are prohibited. * Subjects using any prescribed or over-the-counter concurrent treatment for ADHD. * Subjects with a history of a lack of response to either ATMX or methylphenidate. * Subjects with a history of a serious adverse event to either ATMX or methylphenidate.