Hundreds of thousands of young people are receiving their GCSE results after the biggest shake-up of the exams for a generation.

GCSEs in England have been toughened up with less coursework and exams at the end of the two-year courses rather than throughout.

Some pupils have been so demoralised by the tougher format that they refused to sit the exams this year, while others have shown raised stress levels, according to the National Education Union (NEU) and the Association of School and College Leaders (ASCL).

Eight out of 10 school leaders consulted by ASCL said the new courses had caused less able students to struggle.

One deputy head teacher told the union: “Lower-attaining students are completely demoralised by these new exams. We have an increasing number refusing to attempt mocks and actual exams. This has never happened before.”

Almost all of the more than 500 school leaders contacted by ASCL agreed that the new-style exams, introduced by Michael Gove when he was education secretary, were harder than the previous version. Several said the new format put less able students and those with special educational needs (Sen) at a greater disadvantage.

“Making exams harder doesn’t make kids smarter or more employable. It does make them more stressed, anxious and depressed – especially those from disadvantaged backgrounds,” one senior teacher told ASCL.

Another said it was “soul-destroying” to see well-prepared students struggle to cope. “The difficulty of reformed GCSEs places undue stresses upon students and staff. The sheer volume of examinations in such a short space of time leads to tired and weary students.”

Another asked: “Why does a 16-year-old need to sit between 23 and 27 papers? Why do they need to be examined for seven and a half hours in English?”

The new courses were introduced in 2017 and English and maths were the first to use the harder format and new grading from 9 to 1. This summer another tranche of new courses, including design and technology, were switched to the format.

A spokesperson for the Department for Education said: “Exams are an essential part of ensuring that young people have acquired the knowledge and skills they need, but should never be at the expense of a young person’s wellbeing. We trust schools to work with parents and support young people so they do their best.”

Geoff Barton, the ASCL’s general secretary, said the findings showed that the new GCSEs had sacrificed the interests of vulnerable students in favour of the most able. “In the longer term we simply must review the exam system to find a more humane way in which we can assess the abilities of young people and prepare them for their lives,” he said.

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The NEU polled more than 600 members who taught GCSE subjects in England, and more than seven out of 10 said their students’ mental health had worsened since the new exams were introduced.

Teachers were divided over whether the new GCSEs better measured student ability compared with the previous format. While 54% said the new exams were less accurate, 40% said they were either the same or more accurate.

Teachers told the NEU the harder content was causing pupils to “switch off” and lose interest in coursework. “It is just focused on memorisation rather than engagement and application. There’s no joy in learning any more,” one said.

The survey also found that more schools in England were starting GCSE courses in year 9, three years before exams are taken in year 11.

Wales and Northern Ireland have also changed their exam systems. Northern Ireland has introduced a new C* grade this year to align its grades with the 9-1 system used in England.