The summer holidays, allowing weeks of respite from the stresses and struggles of the classroom, have long been regarded as sacrosanct by the world’s teaching profession. But radical plans to cut the summer break and spread holidays more evenly throughout the year have been proposed by the UK’s biggest headteachers’ union.

Although politicians have in recent years grown increasingly keen on providing the flexibility to change the traditional three-term academic year, schools have largely remained stubbornly resistant to the idea.

However, proposals by the NAHT union could lead to members ditching the six-week break and allocating more holiday throughout the year to ease the pressure on teachers. The plans are the most significant move so far towards altering school terms on a widespread scale.

The proposals, due to be discussed at the union’s annual conference in Birmingham this weekend, are likely to provoke impassioned responses from all sides, and will highlight an issue that has been debated internationally.

Teachers in England and Wales, along with those in Germany and Denmark, already have the shortest summer holidays in Europe. At six weeks, the break is less than half the length of the holiday in countries including Bulgaria, Estonia, Italy and Turkey, where schools close for 13 weeks each summer. High-performing Singapore shuts its schools for seven weeks and the US has a three-month summer vacation.

In a wide-ranging manifesto on the future of education, the NAHT argues that existing term structures make it difficult for teachers to “reduce their hours to a manageable level under current budgets”. “A different pattern of holidays might help teachers, parents and pupils,” it continues. “We should debate more frequent, shorter holidays.”

Academic research suggests that long summer holidays have a detrimental effect on children’s academic performance, with young people forgetting some of what they have learned.

One of the key research papers, a 1996 meta-analysis of 39 US studies, found that at best students showed no academic growth over the summer and at worst lost one to three months of learning. Learning loss was greater in maths than in reading, and disadvantaged students were disproportionately affected, losing about twice the ground of other pupils in reading.

A more recent US study, published in 2007, followed people between the ages of 6 and 22. The research team from John Hopkins University in Baltimore found that two-thirds of the reading gap between disadvantaged 13-year-olds and their peers could be explained by summer learning loss.

The NAHT is also suggesting that school holidays should be staggered in different parts of the country in order to “break the high cost of holidays” for parents and teachers. And it is calling for a legal cap on the total number of hours worked by teachers per week during term time.

Russell Hobby, the union’s general secretary, said the proposals had been drawn up to reduce the “stress and workload” faced by teachers. “They are exhausted by the end of term,” he explained. “The current system is damaging to the health of teachers. Staggering the holidays could ease the pressure on them. However, the long summer break is a key feature of the school year, and it’s not a universally popular idea.”

Stephen Watkins, headteacher of Mill Field Primary School in Leeds, would be wary of cutting the summer break. “Children need time to assimilate what they’ve learned. I think shorter breaks are not necessarily the way to go,” he said. “You could argue there is a dip after every holiday - there is a dip after a weekend. But I think there are other things in life that children should be doing, rather than facing this constant pressure.”

In England, schools that govern their own admissions, including academies and free schools, can already set term dates as they wish. The power will be extended to all state schools from September 2015. Thus far, significant changes have been made only by individual schools.

Djanogly City Academy in Nottingham, for example, has five terms of eight weeks separated by two-week holidays, with a four- or five-week summer break. Plans by the local council to impose a similar term structure on all schools in the city were withdrawn after opposition and strikes by teachers, although a five-week summer holiday has now been introduced.