Deaf pupils will lose a quarter of their marks in some exams if they cannot pass listening tests, in an unforeseen consequence of laws to help disabled people.
Changes to GCSEs and A-levels, due in the autumn, have been described as perverse and bizarre by campaign groups.
Deaf pupils do not take listening tests in exams such as French GCSE, where the aural section counts for 25 per cent of marks. Instead they are given a grade calculated from marks for the rest of the exam. Some candidates also use assistants so they can lip-read.
Exam boards plan to scrap both provisions to meet the disability discrimination Act 2005, which will affect exams from 2007.
The boards say it will mean that pupils with different types of disabilities are not treated differently from others.
The National Deaf Children's Society said the move discriminated against the UK's 35,000 deaf children. Susan Daniels, NDCS chief executive, said:
"This is a farcical interpretation of legislation that was intended to make the situation better for the disabled."
The Joint Council for Qualifications, an umbrella body representing exam boards, admitted last September that "it is an unfortunate and possibly unintended consequence of some of the legislation that some individuals who would be exempted without penalty from certain components of the award will no longer benefit from that exemption".
A Qualifications and Curriculum Authority spokeswoman said it was taking legal advice and was committed to ensuring that no disabled candidate is discriminated against and that there were arrangements to ensure maximum access to qualifications.