Many adults jokingly blame ADHD for their own occasional daydreaming or moments of inattention, but for some children, Attention Deficit Hyperactivity Disorder is far from a laughing matter. The National Institute of Mental Health defines ADHD as a brain disorder marked by an ongoing pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development. More specifically, ADHD affects the executive functioning skills of the brain – functions like concentration, organizational skills, and impulsivity.