Almost 30,000 pupils in the North received record GCSE results, but their success has been overshadowed by a marking blunder.
An internal investigation has begun after it emerged that almost 1,000 students received wrong grades in their home economics GCSEs due to wrong marking boundaries being applied.
The North's main examination body, the Council for the Curriculum Examinations and Assessment (CCEA), yesterday admitted new AS level grade boundaries rather than GCSE guidelines had been used to mark the exams. The amended mistake may improve results of around 140 students from A to A*, but will lower the grades of more than 800 other pupils.
The CCEA's chief executive, Mr Gavin Boyd, apologised for the distress and said he would not rule out disciplinary action once the investigation was concluded.
"I am not going to put up any excuses. It shouldn't have happened and we take full responsibility," he said. However, the mistake did not take away from the fact that this year's GCSE results were the best ever and evidence of a steady improvement by pupils in the North, he added.
The exams, taken by 16-year-olds, confirmed last week's A-level results trend of girls outperforming boys. In total, 7 per cent of pupils - 9 per cent of girls compared to 5.3 per cent of boys - achieved top A* marks, an improvement of 0.4 per cent on last year.
Some Northern Ireland students have to wait until tomorrow when they receive exam results marked by examination boards in England and Wales. While no figures comparing local performances were available yesterday, Mr Boyd said he expected the trend of Northern students "significantly outperforming" their peers in England and Wales to continue.
Overall, there was an improvement in A* and A grades from 22.8 per cent to 23.5 per cent, while grades in the A* to C range rose to 72.2 per cent from 71.6 per cent last year. Girls outperformed boys across the grade range with 10.2 per cent more - 28.7 per cent compared to 18.5 per cent of boys - achieving A* or A marks.