<P> The word quadmester or quadrimester is occasionally used to mean either four months or (more commonly in modern American usage) a quarter of a year . </P> <P> In the United States, the K--12 school calendar is determined by the individual states, and in some cases by the local school district, so there is considerable variation . The academic year typically consists of two 18 - week semesters, each divided into two nine - week marking periods (or quarters) or three six - week marking periods, and constituting 170 to 186 instructional days (with an average of 180). An instructional week is five instructional days, measured Monday--Friday at all public and most private schools; Saturday--Wednesday or Sunday--Thursday at Muslim private schools; and so on . Grades are usually reported per marking period, but major examinations are given per semester or per year . </P> <P> The traditional start date for the school year has been the Tuesday or Wednesday right after Labor Day . Though some schools still keep this tradition, many schools now start in the last two weeks of August and some schools (especially private ones) may start as late as the end of September or the first week in October . There are also some schools, especially in the southern tier of the United States, that begin at the end of July and early August . The school year ends 40 to 42 instructional weeks after it begins (usually around late - May or June). </P> <P> School holidays in the United States vary by jurisdiction . They include federal, state, and local holidays, all or only some of which may be observed by an individual school district . In addition to these legal holidays, there are vacation periods of varying length . Almost all schools observe the Thanksgiving holiday, and extend it to include the day after Thanksgiving (Black Friday) since it is a Friday . There is usually a recess of about one to two weeks during the winter holiday period at Christmas and New Year, with a spring break in March or April that is usually correlated to the holidays of Easter and usually Passover . </P>

When does the academic year start in america
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