A study published in the May 2005 issue of the journal Pediatrics found that children with Developmental Coordination Disorder (DCD)--which has substantial overlap with ADHD, dyslexia and autism--had dramatic improvement in their ADHD-related symptoms after taking essential fatty acid supplements for three months. The symptoms that improved included hyperactivity, restless and impulsive behaviors, inattention, opposition, cognitive problems, and anxiety, and their performance on spelling and reading tests also improved, with no adverse side effects. Essential fatty acids like omega 3 fatty acids formed a much larger part of the Paleolithic diet than today's standard American diet (SAD).
A 1999 review of studies found that most of the evidence pointed to a link between ADD and diet and that the food industry was ignoring the growing body of evidence:
Studies Show that Diet May Trigger Adverse Behavior in Children
HHS urged to Recommend Dietary Changes as Initial Treatment
WASHINGTON - In a  review of two dozen scientific studies, the nonprofit Center for Science in the Public Interest (CSPI) contends that food dyes and certain foods can adversely affect children's behavior. CSPI, in a 32-page report titled "Diet, ADHD, and Behavior," charges that federal agencies, professional organizations, and the food industry ignore the growing evidence that diet affects behavior.
The report cites 17 controlled studies that found that diet adversely affects some children's behavior, sometimes dramatically. Most of the studies focused on artificial colors, while some also examined the effects of milk, corn, and other common foods. The percentage of children who were affected by diet and the magnitude of the effect varied widely among the studies. Six other studies did not detect any behavioral effect of diet.
"It makes a lot more sense to try modifying a child's diet before treating him or her with a stimulant drug," said Dr. Marvin Boris, a pediatrician in Woodbury, New York, whose 1994 study found that diet affected the behavior of two-thirds of his subjects. [...]
Researchers have also found that 79% of hyperactive children improved when suspect foods (foods that included sugars, artificial colorings and flavorings and foods that seemed to cause allergic reactions--including dairy products, soy products, chocolate, wheat, oranges, eggs, legumes, mushrooms, and yeast containing foods) were eliminated from their diets, and that their symptoms worsened again when the foods were reintroduced. (March 9, 1985 issue of the British Medical Journal, Lancet).
As with autism and so many other modern illnesses and syndromes, accumulating evidence strongly suggests a link between ADD/ADHD and diet. This could help explain the recent rapid increase in ADD/ADHD cases, which coincides with increases in obesity, type 2 diabetes and other disorders and diseases of civilization. The Paleolithic/evolutionary model of nutrition could help explain a host of chronic modern illnesses.
Unfortunately, there aren't many large industries that would fund Paleolithic nutrition research the way there are for research seeking to demonstrate the benefits of modern foods like whole grains and low-fat dairy. There isn't a lot of profit to drive Paleo research, so humanity will likely have to suffer a lot longer before these findings become widely known and more thoroughly researched.