Pupils face being given a national ranking from first to up to nearly 90,000th in A-level exams to help universities select the brightest candidates from thousands of top-grade passes.
The move was floated by the Education Secretary, Michael Gove, as one of a series of radical measures to revamp A-levels, but parents' leaders said they were "alarmed" by the proposal and warned it would lead to increasing numbers of appeals against exam results.
One more mark could mean the difference of up to 1,000 places in the ranking.
"You can imagine a kid being really chuffed to get an A-level, only to be choked at being told 'actually, you're only 500th in the country in this exam'," said Margaret Morrissey, of the parents' pressure group Parents Outloud.
In his speech, Mr Gove said some exam boards were debating the idea of ranking pupils. Other moves outlined by Mr Gove in a speech to Ofqual, the exams watchdog, included placing a limit on the awarding of A* grades, so that only a fixed percentage were handed out every year.
The rankings would indicate which pupils were top in the country in each subject – and also bottom.
In the same way as A-level grades, they could be passed on to universities, schools and individual pupils.
At one school where ranking has already been trialled, Burlington Danes academy in Hammersmith, London, it had improved pupil performance and led to students rating their teachers.
"Parents love it," he said, "because they give information that they'd previously been denied. In the past, parents asked 'how has my son done?' and they would receive the reply 'he's a lovely boy'. Now they accurately knew where he stood."
Results had also improved.
"So if ranking can achieve that in one school in White City, if additional data and transparency can generate those beneficial results, is there a case for exam boards publishing more data about the performance of students rather than less?"
On limiting A* grades, he added: "We can't go back to a situation where all exams are graded on the basis of norm referencing (fixing the percentage pass rate, as happened in A-levels prior to 1980)."
However, he added: "Could it be the case that – while we award As, Bs and Cs on the basis of criterion reached, is there a case for exploring whether or not A*'s should be allocated only to a fixed percentage of candidates? I would like to see that debate explored and engaged with."
The conference was told by Glenys Stacey, chief executive of Ofqual, that "most recent studies" showed evidence of exam papers being less demanding.
A soon-to-be-published report on A-level chemistry will reveal that the exam was less demanding in 2008 than 2003.
There were, she said, many more shorter questions that relied on candidates' memories rather than knowledge.
Professor Robert Coe, from Durham University, addressing the same conference, said analysis showed A-levels had suffered from grade inflation for the past 20 years.