Fewer than a quarter of American high-school students now take what is colloquially known as “gym class” daily, down from nearly half five years ago. Four of the 50 states have done away with the requirement to provide PE completely and two more - Massachusetts and New Jersey - may let local districts reduce or eliminate it in favour of history, geography and other subjects.

Advocates of PE say giving children the chance to be active during the school day is increasingly important at a time when many get no more exercise than it takes to play computer games or watch TV.

Judy Young, director of the National Association for Sport and Physical Education, said: “In this country, a lot of our kids are latchkey kids. ” Her preferred solution is not to make room for some subjects by eliminating others, but to extend the length of the school day and the school year. Several states are considering that option.