Attention Deficit and Hyperactivity Disorder
Let us begin with what several families in America deal with on a regular basis; Attention Deficit and Hyperactivity Disorder.  About 2%-3% (some sources report as much as 6%) of the United States population has ADHD, also commonly diagnosed simply as ADD(the patient's problems lie less within hyperactivity and more with abilities to focus). 

According to the National Attention Deficit Disorder Association, there are three main characteristics used to diagnose children with ADHD: Distractibility, impulsivity, and hyperactivity.  Common sypmptoms include difficulty sitting still, and inability to stay focused and pay attention, forgetfulness, and absentmindedness.  ADHD can also be said to contribute to, or in some way coincide with, depression and anxiety and conduct disorders among other things. 

ADHD persists throughtout life and is most likely not caused by environment effects such as poor parenting or too much sugar, though it is not known exactly what causes the disorder.  Most psychologists would agree that it is probably some form of a neurobiological problem- simply put, it is the inability to stop receiving messages from different stimuli.  Treatment is usually handled with the aid of drugs such as Ritalin or Adderal, though neurotherapy is another option which works in most cases of ADD/ADHD.
Links
For more information on ADD/ADHD visit these sites:
National Attention Deficit Disorder Association
official website
Children and Adults with Attention Deficit Disorder(CHADD)
official website of the support organization
American Academy of Pediatrics
Practice guideline article- Diagnosis and Evaluation of the Child with Attention-Deficit/Hyperactivity Disorder.
Dr. John Shackelford
private practice website with some discussion on neurotherapy
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Scientific American Article- "A new theory suggests the disorder results from a failure in self-control."  Almost all the links at the end of the article are helpful as well.
National Institute of Mental Health- journal publication online
Cambridge Center for Behavioral Studies- description of the disorder as well as a link to an article from the Surgeon General.
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