North Carolina State researchers have found that younger children are 50% more likely to received a diagnosis of Attention Deficit Hyperactivity Disorder (ADHD).  These children were often born right before the kindergarten cutoff date.  It is suspected that small differences in age can result in huge differences in development, resulting in children who have a difficult time paying attention for extended periods of time.  The really sad part is that a lot of these kids have been prescribed medications that were not necessary as they were misdiagnosed with ADHD.