The exams system in England is unwieldy and becoming unsustainable because of a record number of pupils challenging their results, head teachers warn.
A record number of pupils queried their GCSE results last year
Last year 45,000 pupils - one in 14 GCSE students - queried a result.
And the National Association of Head Teachers (NAHT) says the extra work and the cost of the appeals is pushing the exam system towards collapse.
The Qualifications and Curriculum Authority (QCA) denies the claims insisting it is fair on all pupils.
Last year, one in four of all the 45,000 GCSE pupils who challenged their exam mark ended up being upgraded.
The QCA said the number of marks regraded was relatively small, given that six million GCSE papers were marked last year.
NAHT Deputy General Secretary Carole Whitty said: "If one in four are getting regraded then it does make you wonder if there are a load of students who - had they put their papers in for remarking - whether they might have been regraded too.
"And this is an important message that is getting back in to the system. It's a very destabilising situation."
She added: "If you had a system with well designed examinations and strong marking there shouldn't be any appeals at all, or maybe just a tiny handful," she said.
"We're really creating a system which is very unstable."
Meanwhile, Richard Cairns, headmaster of Brighton College, expressed concerns about "the increasing number of children who seem to be getting marks that are out-of kilter with what we anticipate".
"We're having to go through those marks very carefully with the children concerned and lodge more and more appeals," he said.
The BBC's Cathryn Curran said critics claim more mistakes are being made at the marking process because of the growing number of exams.
There are also concerns over the cost of an appeal - on average it costs £45 to appeal against a GCSE result, and up to £35 for each A-level unit.
Our correspondent also says some schools have told the BBC they do not appeal because they cannot afford the costs involved.