The State Examinations Commission (SEC) is investigating a possible breach of protocol, after an examiner was seen marking a Leaving Certificate paper on the DART.
Claire from Blanchardstown in Dublin says she could see the student number on the paper, which was clearly visible being corrected on a packed train during the morning rush hour.
The SEC says examiners are given specific training that all exam material is highly confidential, and should not be accessible to the public.
It says any breach of duty is taken very seriously, and can result in the immediate termination of a contract with an examiner.
Claire says she saw the teacher marking the paper while they were waiting for a train in central Dublin.
Craig NcHugh is honourary president of the Irish Second-Level Students' Union (ISSU).
He told Newstalk Lunchtime he believes the paper in question should be re-checked.
