The purpose of this study is to test if the investigational medication ABT-089 is a safe and effective treatment for children with Attention-Deficit/Hyperactivity Disorder or ADHD.

Inclusion Criteria:

• Have voluntarily signed an informed consent form
• Meet diagnostic criteria for attention-deficit/hyperactivity disorder (ADHD) based on detailed evaluation and interview with parent(s)
• First grade or higher in a school setting 3 days/week
• Subject is generally in good health based on medical history, physical examination, clinical lab tests, and ECG
• Subject weighs at least 37 pounds (17 kg)
• Female subjects of childbearing potential must have a negative urine pregnancy test at screening and baseline and agree to comply with applicable contraceptive requirements
• Subject and parents have been judged by the study doctor to be reliable to keep required appointments for clinic visits and all tests, including blood draws, and examinations

Exclusion Criteria:

• Subject is not functioning at an age-appropriate level intellectually
• Subject has a current or past diagnosis of bipolar disorder, psychosis, autism, Asperger's syndrome, or pervasive developmental disorder
• Current diagnosis of obsessive-compulsive disorder, eating disorder, anxiety disorder or depressive disorder requiring treatment of any kind
• Subject has a history of significant allergic reaction to any drug
• Subject requires ongoing treatment with any psychiatric medication
• Subject has a serious medical condition, seizure disorder (except febrile seizures as an infant), or history of substance abuse or dependence