Around 20 per cent of GCSE and A-levels taken by students in Ulster this year were issued by external exam boards rather than the Northern Ireland Council for the Curriculum, Examinations and Assessment.
The CCEA has no comparative figures, but is convinced there is a trend away from its exams. A marketing campaign to entice more students to sit more exams with the board has been launched.
A spokesman blamed the drift away from the board on its small size and the limited range of subjects it offers. But he dismissed the suggestion that the board's qualifications were less well regarded by universities and employers in England, Wales and Scotland, saying he was confident the decline could be reversed.
The board this week recorded improvements in GCSE results - announced well ahead of the results for England and Wales - and in A-level results.
A total of 22 per cent of students received an A grade in their A-levels and 92.7 per cent achieved grades A to E - a 2 percentage points increase on last year's results in both cases.
But the number of candidates sitting A-levels fell by more than 500 from last year to just over 10,200.
At GCSE, 20.5 per cent of students received grades A* and A compared with 19.3 per cent last year. Almost 70 per cent of pupils scored grades A* to C (a 2 point increase from last year) while 97.6 per cent scored grades A* to G - also a slight improvement.
The number of candidates has dropped by more than 1,000 over the past two years while the number of papers issued has fallen by almost 9,000.