Sugar, that ubiquitous substance, white, sweet and highly addictive was first discovered by Western Civilization during the medieval Crusades. As these "knights" were descending upon Jerusalem to wreck holy havoc, they spotted fields of sugarcane. Tasting this and finding it too good to pass up, they brought these plants back to Europe, and the rest is, well, history. It was known to be dangerous within a few years, teeth rotted, headaches and stomach aches were common. The wealthy aristocracy was quickly addicted and once it became affordable, the common man was able to use it. Even in the early history of this nation, sugar was sold behind the counter, it was known to be dangerous.
Sadly, sugar's grip on people became stronger as everyone could find it and use it. The sugar industry as it has grown over the last century began lobbying Congress as well as the medical community. As recently as the 1960's, the Sugar Lobby paid more than $50,000 to a group of Harvard physicians to write a paper on the causes of heart disease, dismissing sugar as a contributor and putting the blame instead on fat. The hallowed New England Journal published this paper and it has taken us 50 years to figure out the scam (news of this event broke just this year, 2016).
While physicians like myself were telling their patients to worry about fats which were thought to be the main cause of coronary artery disease (heart attacks), the real enemy was being consumed in larger and larger amounts by everyone including small children.
Breakfast cereals, processed by the cereal industry and promoted by strong lobbyists, became the food of school lunches and pretty much every child's breakfast at home. Most cereals contain sugar as its number one or two ingredient. Thus our children head off to school charged by sugar, only to crash within an hour or two. Children may begin acting out, spacing out and find themselves paying less attention to school and getting themselves in trouble.
Those who don't react to sugar this strongly (more on this may be found on another page on this website) will still find themselves losing energy and indeed their school performance suffers.