Ministers face fresh calls to reform A-levels amid predictions of another record number of students scoring top grades.
As more than 260,000 students prepared to receive their results on Thursday, headteachers called on the Government to replace the "gold-standard" exam with a new diploma.
One expert predicted another rise in the overall pass rate this year, with even more teenagers getting As.
And the National Association of Head Teachers warned more schools were now turning away from A-levels in favour of the International Baccalaureate, which offers a broader range of subjects and is seen as more challenging.
In 1982 only 8.9 per cent of students scored As at A-level but last year 22.4 per cent achieved the highest grade, said Professor Alan Smithers, director of the University of Buckingham's Centre for Education and Employment Research.
The A-level pass rate in 1982 was 68.2 per cent but in 2004 it was 96 per cent, said Prof Smithers.
"It would be reasonable to suppose that we are going to get quite close to 96.5 per cent this year," he said.
He said pupils were using AS-levels - taken in the first year of the A-level course - to find out which subjects they were good at.
Then they chose their best subjects to study for the A2 section of A-levels in the second year, he said.
These changes, which came into force five years ago, had given "a tremendous boost" to the pass rates, he said.
"Clearly the new arrangements make it easier to get higher grades.
"That doesn't necessarily mean that the content has been changed.
"It's easier to take a course in bites rather than studying for two years and integrating it and developing an understanding across the subject."
It was now time to make the exams harder, said Prof Smithers.
"The tremendously high proportion getting these top grades in these subjects underlines the need for tougher questions so that the really talented distinguish themselves from the very able," he said.
David Hart, general secretary of the National Association of Head Teachers, said it was not "easy" to get an A.
But he warned that more schools were dropping Alevels and opting for the International Baccalaureate diploma.
"More and more schools will be looking towards the International Baccalaureate and will be abandoning Alevels particularly for the more able pupils rather than wait for the Government to decide that its response to Tomlinson needs to be changed.
"We cannot afford to sit about waiting for the next review in 2008."
Education Secretary Ruth Kelly has promised to look again at the option of introducing a new diploma covering A-Levels in 2008.
Ms Kelly provoked anger in February when she rejected former Ofsted chief Sir Mike Tomlinson's plan for replacing GCSEs and A-levels with a new set of diplomas combining academic and vocational courses. The Tomlinson plan won widespread support among teachers, school inspectors, and exam chiefs.
Martin Ward, deputy general secretary of the Secondary Heads Association, said: "Every year it's depressing that we get a chorus of gloom when young people work really hard and have really good results."