The traditional six-week school summer break should be cut to stop teacher exhaustion and reduce holiday prices, heads are suggesting.
Instead, holidays should be spread more evenly throughout the year.
The union is considering the proposal as part of a new education manifesto it is drawing up at its annual conference this weekend ahead of next year's general election.
Other propositions up for discussion include reform of school admissions to ensure that the poorest pupils are given priority for places - including at private schools, and a cap on teachers' total weekly working hours.
The draft manifesto also includes calls for the Pupil Premium - extra money for the poorest pupils - to be extended to two-year-olds and for staff working in early years education to have qualified teacher status.
Under the current system, state school pupils in England and Wales usually get two weeks off at Christmas and Easter as well as six weeks in the summer, and three, week-long half-term breaks.
But the system has been under the spotlight recently, in part due to rising concerns about high holiday prices when children are off school.
NAHT general secretary Russell Hobby said that there has been much debate and evidence recently over whether children suffer "learning loss" over the long summer holiday, although much of this comes from the United States which operates a different system from England and Wales.
"One of the things that I'm concerned about is whether the current structure of holidays is also healthy for the people who work in schools as well," he said.
"It seems like, at the end of term, everyone is ready to drop and that actually, not reducing the amount of holiday but distributing it more evenly across the year might be one solution to that."
Under government reforms, academies and free schools already have the freedom to set their own hours and term times and this is being extended to schools still under local council control.
Mr Hobby said that the union did not have "any particular liking" for every school setting its own dates as this could cause problems for families with children at more than one school.
He added: "We would like to see local or regional co-ordination, but at that point you could also have the opportunity to have a staggering of holidays around the country.
"So if different parts of the country within local authority boundaries or regional boundaries had slightly different holiday times I think that would ease the pressure on the prices of holidays as well."
Stephen Watkins, a primary headteacher from Leeds, said he was against changes to the six-week holiday.
"There doesn't seem to be the same call for independent schools to give up their eight-week holidays," he said.
Mr Watkins said that teachers often come in to school during their holidays to prepare for the forthcoming term and that children "need time to assimilate the learning that has taken place".
Education Secretary Michael Gove for England had previously called for longer school days and terms, warning that the current system is out of date, and fit for the agricultural economy of the 19th century.
In a speech last year, he claimed that pupils are at a ''significant handicap'' compared with youngsters in East Asian nations who benefit from extra tuition and support from teachers.
But the reforms have proved controversial, with some teachers' unions arguing that school staff and pupils already spend long hours in the classroom.