June , July and August. 😉
However,
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. Plus, students in other industrialized countries have more instructional time. The Israeli academic year lasts 216 days, and kids in Japan plug away for a whopping 243 days per annum. (Slate)