A Study of Dex-methylphenidate Extended Release in Children (6-12 Years) With Attention-Deficit/Hyperactivity Disorder (ADHD)

Inclusion Criteria: * Male and female subjects aged 6-12 years, inclusive. * Subjects meeting the DSM-IV criteria for ADHD of any type, as established by the K-SADS-PL (Kiddie Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version). If a DSM-IV-defined ADHD diagnosis is difficult to establish due to possible co-morbidity, the subject will not be enrolled into the study. * Subjects should be on a stabilized total daily dose or nearest equivalent of 40-60 mg methylphenidate or 20-30 mg of d-methylphenidate for at least two weeks prior to screening visit (Concerta® 36 mg and 54 mg is allowable) Exclusion Criteria: * Parent or guardian unable or unwilling to complete the Conner's ADHD/DSM-IV Scale for Parents (CADS-P) and the Daily Diary Card * Diagnosed with a tic disorder or Tourette's syndrome * History of seizure disorder * The presence of a known medical condition that would preclude the use of methylphenidate. A history (within the past year) or presence of clinically significant cardiovascular, cerebrovascular, renal, hepatic, gastrointestinal, pulmonary, immunological, hematological, endocrine, or neurological disease * ALT, AST, GGPT or serum creatinine greater then 2X the ULN at Screening * A history of psychiatric illness or substance use disorder (e.g., schizophrenia, bipolar disorder, autism, abuse or dependence, depression, severe Conduct Disorder or severe Oppositional defiant disorder) * Subjects who have participated in an investigational trial within the past 4 weeks (28 days) are excluded * Subjects who are currently taking antidepressants or other psychotropic medication * Subjects who have initiated psychotherapy during the three months prior to randomization * Subjects with a positive urine drug screen * Subjects who have a history of poor response or intolerance to methylphenidate or d-methylphenidate Other protocol defined inclusion/exclusion criteria may apply