More than 2,500 students will start their delayed Leaving Cert this evening.
Biology is the first subject - with the exam starting at 5.30pm.
They are scheduled to take place on evenings and weekends until December 11th.
Guidance counsellor Donnchadh O'Mahoney says most of those sitting the exams are already taking college courses.
"Some of the students sitting the exams, actually the majority, would have been offered college places this year and they'd have started college places.
"The reason they're going back to sit these exams is that the probably wanted college place further up on their CAO list that they really wanted.
"So they probably these and are studying in these, and said 'look I'll take these exams, if I do better and get offered another one for next year, if not nothing lost.'"
