In Britain, an academic year usually runs from September of one year through to June or July of the following year, with the time split up into three terms. In an academic year, a student must complete a set number of semester hours. Academic years vary from school to school and even from educational program to educational program at the same institution.
When the United States was a primarily agrarian society, children were needed during the Northern Hemisphere summer months for farm labor. Summer is still a popular time for family vacations, and most school districts have a 2 or 3 month summer vacation. K-12 school years typically run from late August or early September until May or June, depending on the length of the year and number of holiday, vacation, and snow days occurring during the year. The year is divided into two semesters or four quarters, typically with a report card issued to students' parents at the end of each.
An academic year at a college or university typically includes a fall and spring semester, with a shorter optional summer session. Many also have a short optional winter session. Some operate on a trimester calendar.
Continuing education classes (often available at community colleges and private "boot camp" style schools) are often shorter and start throughout the year with no particular seasonality.
Public elementary and secondary schools averaged (at the state level) between 171 and 184 school days in the 2007-08 academic year. Different states have different legal minimum requirements for instructional days and hours per year.