The row over the quality of A-levels is continuing ahead of the annual release of results on Thursday.
Ministers stress that only one in 10 A-level students gets three As
Figures are likely to show that almost all candidates passed, with about 23% of entries getting the top grade.
Ministers and exam officials have moved to defend standards - with schools minister Jim Knight insisting A grades are not "handed out like sweets".
Former chief inspector of schools, Chris Woodhead, said A-levels were "simply not fit for purpose".
Mr Knight said those who equated rising pass rates with "dumbing down" were not only doing young people a disservice, they were taking a simplistic view of the system.
"There is a general misconception that the A-level has become impossible to fail and that A grades are handed out like sweets," he said.
"This, like many myths surrounding the exams, is nonsense."
Meter or filter?
He said that last year about 24,000 A-level candidates achieved three or more A grades - 3.6% of the total year group.
"So out of the class of 30 that started secondary school aged 11, just one will go on and achieve the prized three As at A-level," he said.
It was true that more people got As today than 20 years ago - but that was because there used to be quotas for the number of grades awarded at each level.
"The simple question is: should the exam system reward people for what they have achieved, or act as a filter to reduce the number of people who can achieve a particular grade?
"My view - and I believe that of students, parents, universities and employers - is that exams should measure success, not put a cap on it."
Former chief inspector of schools and now education professor, Chris Woodhead, said that, in his view, the syllabuses of GCSEs and A-levels were "less challenging" compared with those of 20 years ago.
He criticised the system of dividing the qualification into modules whereby a test - which can be resat - is sat at the end of each module - a method which he felt made it easier than the traditional "terminal" exam.
He added: "We now have an A-level where almost one in four are getting A grades. The exam is simply not fit for purpose.
"It has been dumbed down to the point where it is not identifying the best candidates.
"All now must have prizes and the fact that all have prizes means the prizes are worthless."
Head of the Qualifications and Curriculum Authority (QCA), Ken Boston, insisted there had been continued rises in standards and it was simply "not true" that exams had got easier.
He said: "We maintain the height of the hurdle assiduously and more and more young people, thanks to the improving quality of education are jumping that hurdle."
Mr Knight did concede there was a fundamental problem: as more students get top grades, universities find it harder to distinguish between them and routinely reject applications from well-qualified candidates.
So the system is being changed again.
From next year, universities will see the grades for each of the six units that make up an A-level, as well as the overall final grade.
To provide more challenge, students are likely also be asked to produce an extended project, and to face tougher questions in their A-level papers.
These two approaches are being piloted by the QCA.
"These changes will make sure that every young person is able to fulfil their potential and get a grade that more finely accords with what they have achieved," Mr Knight said.