The Education Minister has been urged to rethink his decision to stick with letter grades for GCSEs after two English exam boards pulled out of Northern Ireland.
DUP MLA Peter Weir blamed John O'Dowd's "folly" after the largest exam boards in England - the AQA and the OCR - announced their withdrawal.
Mr O'Dowd said in November that a numerical system being adopted in England from September would not be introduced here.
The AQA and OCR were only told of this decision afterwards and not consulted beforehand. Last night the boards said they would not operate two grading systems, and added they would no longer offer GCSEs here, although A-levels will continue.
Around a quarter of GCSEs sat here are taken through the AQA and OCR boards. The remainder of exams are set by local exams board the Council for the Curriculum, Examinations and Assessment (CCEA). Mr Weir said he feared Mr O'Dowd's decision would hand the CCEA a virtual monopoly over GCSEs here.
"The decision by the two largest exam boards in England to pull out of providing GCSE exams in Northern Ireland is disappointing but not surprising," he added.
"It is a direct result of the inflexible approach taken to GCSE grading by John O'Dowd."
He added: "The situation we now have could have been easily resolved by adjustments to our grading system, ensuring it was aligned with grades in England.
"That would have allowed portability and transferability for Northern Ireland. The folly of not making that straightforward adjustment is shown today."
But Mr O'Dowd hit back and accused the English boards of "choosing to put commercial interests ahead of the needs of our young people", and said schools will be advised on the next steps by the end of the month.
"In particular, CCEA will be able to advise on arrangements for those pupils who are already working towards qualifications in maths and English literature provided by these awarding bodies that have now decided to leave us," he said.
"Guidance will also be given on the alternatives available to fill gaps that might emerge in the range of GCSEs on offer as a result of those decisions. In many cases, the variation in subject specifications across awarding organisations is not great, and therefore there will be alternative specifications available for pupils to follow."