Interesting article on Slate about the origins of 3-month summer vacations for American schoolchildren. Apparently, the primary reasons for such a long academic layoff are due to century-old developmental theories, outdated medical concerns, and fiscal limitations.
The now-standard 180-day academic calendar with a long summer holiday didn't come about until the early 20th century. Reformers could have instituted a long break in winter, or spring, but they picked summer for three main reasons. 1) Poorly ventilated school buildings were nearly unbearable during heat waves. 2) Community leaders fretted that hot, crowded environments facilitated the spread of disease. 3) Wealthy urbanites traditionally vacationed during the hottest months, and middle-class school administrators were following in their footsteps.
Obviously, physicians no longer believe that children are too feeble for year-round instruction, and most school buildings now have effective ventilation systems. So why don't we go back to having school in the summertime? For one thing, it's expensive to keep schools open, just like it was in the late 1800s. But some nonprofit organizations argue that the long breaks hinder the learning process. According to the Johns Hopkins Center for Summer Learning, kids score worse on standardized tests in early September than in late June.
Incidentally, while most American kids are only in school for 180 days per year, the Israeli academic year lasts 216 days and kids in Japan plug away for a whopping 243 days per annum. In fact, very few industrialized nations have academic years shorter than ours.