Changes to England's exams system could lead to school-leavers in Northern Ireland being "disadvantaged", teachers have warned.
The concerns were raised after it emerged numbers will now be used to grade GCSEs in England, rather than letters.
The current A* to G system will be replaced with the numbers 1 to 9, with 9 the top grade that can be awarded.
The purpose of the change is to differentiate the different levels of grades.
The shake-up only has implications for exams which are set by boards based in England. However, a significant number of pupils sit exams set by English exam bodies every year in Northern Ireland.
Those pupils could now have a mixture of letter and numbers in their GCSE results – a prospect which is prompting concern.
The new grading system has been described as the biggest shake-up of England's exams system in a generation by exams regulator Ofqual.
While Wales is planning its own reforms to GCSEs, Education Minister John O'Dowd has already said that there is no appetite for scrapping the exams system in Northern Ireland. The possibility of ending GCSEs in the longer term has been left open, however.
Deborah O'Hare, principal of Wallace High School in Lisburn, is concerned about the perceived lack of parity between GCSE grades here and the rest of the UK when reforms in England are introduced.
Around 38% of local school leavers go to universities in England, Scotland and Wales every year.
Ms O'Hare said that a focus on exam standards across the UK had undermined the currency of qualifications such as GCSEs.
"That's really a pivotal issue for us," she said. "How, on the one hand, do we not have significant changes, like in England, but on the other hand have currency?
"We have time, but unless they make changes in Northern Ireland that they have made in England, all this serves to do is undermine the system in Northern Ireland further.
"In Northern Ireland we have a small community and we do not want what's already a minority community to be disadvantaged further by a change like this," she added.
Children currently in their first and second years in England's post-primary schools will be the first to experience the changes – which are being staged and come into effect in 2017.
English and maths will be the first subjects to be affected in 2015. Course work will no longer be used in English language GCSE – which, alongside English literature, will be assessed entirely through exams. Maths will also be assessed solely by exams.
The introduction of a series of changes to 20 GCSE subjects will follow in 2016. Course work is also being scrapped across most subjects.