Controlled studies have measured the effects of sugar consumption on behavior and cognitive performance and failed to find any connection. See for example this meta-analysis. There have even been interesting studies where parents were asked to observe kids behavior. When the parents thought the kids had eaten sugar, they reported changes in behavior--even when the kids had actually been given a placebo. See this article for more on the sugar-hyperactivity myth.Read it all and get the links at Nutrition Diva.