Reminds me of that chapter in Nurture Shock on the "lost hour".
Sleep studies performed on children are revealing that a single lost hour of sleep a night can reduce academic performance, affect emotional stability, and increase the incidence of medical conditions such as obesity and Attention Deficit Hyperactivity Disorder (ADHD). They found that a single lost hour of sleep could result in 6th grade children performing at the level of a 4th grader.
http://figur8.net/baby/2009/10/26/nurture-shock-chapter-2-the-lost-hour/