For GCSE, AS- and A-level students, exam season already looms large - and August results day will be etched in their minds, too.

For teachers, who often have performance “judged” against exam outcomes, the importance of the period cannot be overstated.

A recent news item about exam accuracy, however, gives us pause for thought - especially because it was raised in the House of Commons.

How accurate are exam grades?

To summarise: last summer about 1,400 learners at West Nottinghamshire College sat GCSE English language. The college requested reviews of marking for 41 of the grades awarded, resulting in 20 going up one grade, and two making a two-grade leap from grade 3 to grade 5.

From this, the principal became concerned that perhaps other grades that had not been challenged might be wrong, too.

He raised this with the exam board, Pearson Edexcel, which stated that it had carried out “detailed quality assurance checks” and had found “no wider issues with the marking of students’ exams” (see full statement below).

Meanwhile, a spokesperson for Ofqual noted more broadly that “out of 6.5 million GCSE, AS- and A-level grades awarded in summer 2025, 4.6 per cent were challenged and 1.1 per cent were changed following reviews”.

As discussed in Tes last December, Ofqual’s statement that 4.6 per cent of the grades awarded were challenged, and 1.1 per cent changed, is true.

But that certainly does not imply that the remaining 98.9 per cent are right, for this assumes that all unchallenged grades are correct - a fallacy acknowledged in an Ofqual blog, dated 29 September 2014, written by Ofqual’s then chief regulator, (now Dame) Glenys Stacey.

‘Definitive’ grades - and ‘non-definitive’

In fact, Ofqual has, for some years, had good knowledge of the likely number of incorrect grades awarded, whether challenged or not: Figure 12 of its November 2018 report Marking Consistency Metrics - an update shows, for each of 14 subjects, the probability of being awarded a “definitive” grade. Ofqual defines this as the grade that would have been awarded had a subject senior examiner done all the marking.

For English language, this probability was about 61 per cent, indicating that 61 of every 100 grades were ”definitive ”, and the remaining 39 were “non-definitive”.

Since a senior examiner’s “definitive” grade is the ultimate authority of “right”, any other “non-definitive” grade must be, in plainer language, “wrong”.

If we applied this to the English language grades at West Nottinghamshire College, it would mean 61 per cent of the 1,400 grades awarded - that’s 854 grades - were ” definitive” or “right”. And 546 grades were “non-definitive” or “wrong”.

Those “non-definitive” or “wrong” grades are wrong both ways with equal probability, so 273 students would have been awarded grades too high, and 273 grades too low. In this category, we know 22 were discovered and corrected.

What about the students whose awards were two grades adrift? Two were discovered. Are there any more?

Ofqual knows the answer to this, too.

At a hearing of the Commons Education Select Committee held on 2 September 2020, Dr Michelle Meadows, at that time Ofqual’s executive director for strategy, risk and research, stated that 96 per cent of GCSE grades were accurate plus or minus one grade.

That number was an average across all GCSE subjects, so, assuming it is valid for English language, it would imply that about 4 per cent of West Nottinghamshire College’s 1,400 students were awarded a grade at least two grades wrong.

That’s about 56 students, 28 of whom have certificates showing a grade at least two grades too high, and 28 two grades too low. Of which two were discovered.

Planning ahead

The college’s principal was, therefore, right to be concerned that more students had been awarded wrong grades than had been discovered by a challenge.

This issue, of course, goes far beyond the grades for one college in one subject.

For schools, it underlines the reality that, come exams results days, it is worth casting an analytical eye on the outcomes achieved by students and being ready to consider a challenge if things don’t quite look right.

Dennis Sherwood is the author of Missing the Mark: why so many school exam grades are wrong, and how to get results we can trust