More than one in four A-levels are expected to be awarded at least an A grade this year, but pass rates are set to stall, it has been predicted.
In a bid to avoid grade inflation, the exams regulator Ofqual has told exam boards they will be asked to justify results that differ wildly from previous years.
It means that the proportions of students awarded top grades are unlikely to increase greatly from 2011 levels.
Professor Alan Smithers, director of the Centre for Education and Employment at Buckingham University said he would expect to see the proportion of exams awarded an A* rise only slightly, from 8.2% in 2011 to around 8.3%.
"If Ofqual had not introduced 'the principle of comparable outcomes' to nail inflation, I would have expected the percentage of A* to have gone up by quite a lot, say to 8.5% or more," he said.
The A* has now been awarded for three years, schools are used to preparing pupils to achieve it, and universities are asking candidates for the grade, he said.
But Ofqual has said it wants to see a distribution of grades similar to last year, which were tied to 2010 A-level results, Prof Smithers said.
Last summer 27% of A-levels were awarded an A* or A, the same as in 2010, It was the first time in more than a decade that the results had remained static.
"This year, it could go either way, but I am guessing that Ofqual will hold the percentage of A*-A close to 27%, but because there are good reasons for it happening allow the percentage of A* to increase say to 8.3%," Prof Smithers said.
"The interesting thing now is we know that what Ofqual is intending is that the pattern of results this year should be more or less the same as last year. Other things being equal, they'll be asking the exam boards stiff questions if there's a big movement from the results last year."