Some 6,000 16-year-old students in the North will have to take a special history test next week after the paper they were due to sit this morning was leaked.
The Council for the Curriculum Examinations and Assessment (CCEA) said it decided to reschedule the General Certificate of Secondary Education examination because of a breach of confidentiality. New papers for both higher and foundation tiers of the subject are being sent to 150 schools. Ms Catherine Coxhead, chief executive of the council, which is responsible for all public examinations in the North, said it was investigating thoroughly what had happened.
It was already clear that pupils in "more than one school" had seen some of the questions.
In deciding to rearrange the examination, her priority was to ensure all candidates were treated fairly.
She suggested there was a deliberate breach of confidence when she said the problem was not a mistake but a leak.