Hundreds of thousands of teenagers are about to find out their GCSE results, with almost all results in England to be graded from 9 to 1.
The highest grade 9 will be harder to achieve than the previous A*, in a tougher, revised GCSE exam system.
There have been estimates that only a few hundred pupils will be the first to get a clean sweep of grade 9s.
Pupils in Wales and Northern Ireland will continue to get their results graded from A* to G.
About 90% of entries in England this year will be in the new, more challenging form of GCSE. These have more difficult content and are mostly marked on final exams, rather than coursework.
The intention is to pitch the exams at the standard of the highest-achieving countries in education, such as Singapore and Finland.
There will be 20 of the most popular GCSE subjects in England graded for the first time in the numerical format.
These include history, geography, sciences and modern languages, all of which have been designed to be more difficult.
About a fifth of results last year were A* or A grades, but these top results will be more precisely differentiated, with 7, 8 and the highest 9 grade.
There have been forecasts of a dip in the proportion achieving at least the new pass grade 4 – equivalent to the former grade C.
But the exam regulators will want to maintain stability with previous years, and prevent a “guinea pig” cohort from being disadvantaged.
This means that changes to the overall pass rate – combining more than 5 million entries in England, Wales and Northern Ireland – are expected to be relatively small in percentage terms.
This could mean that grade boundaries are adjusted downwards for some subjects.
Last year saw the introduction of the new tougher exams in English and maths – and pupils only needed 18% to get a pass in one of the maths papers.
Malcolm Trobe of the ASCL head teachers’ union has warned that if exams are “excessively difficult” it could send a “demoralising message” to lower-achieving pupils.
“If grade boundaries have to be set very low, this indicates that the exam is so difficult that many candidates have been unable to answer a significant proportion of the paper.
“This inevitably increases stress and anxiety and leaves them feeling that they have done poorly,” said Mr Trobe.
Kevin Courtney of the National Education Union said teachers were “deeply concerned about the pressure and stress these new GCSEs have put on students and school and college staff”.
Sally Collier, head of the exam regulator Ofqual, said: “Students picking up their results today can be confident they have achieved the grades their performances deserve.”
But Chris Keates of the NASUWT teachers’ union said the exam changes had been “rushed” and any comparisons with results in previous years should not “demean students’ achievements”.
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