More than 1,000 schools across the country have extended the calendar by adding at least 10 days to the year or by lengthening each school day by half an hour, research has found.
The average school year in the US, as in Britain, is 180 days. This is much lower than countries such as Japan where many schools have years of well over 200 days.
However since a report titled A Nation At Risk, commissioned by the then President Ronald Regan and published in 1983, US schools have been urged to act upon a recommendation that the school year is increased.
The National Centre on Time and Learning, a non-profit research group in Boston, says that it is only recently that progress has been seen.