Several hundred Junior Cert students were not given their full results yesterday after the Department of Education said it was investigating possible copying in relation to the subject, civil, social and political education(CSPE).
The Department said CSPE grades for 656 students in 41 schools were being withheld pending the outcome of the investigation.
It said a significant level of similarity was discovered in the work presented by candidates in several schools. In some cases the work was identical in almost every respect. The Department emphasised that - so far - no wrongdoing had been proven, although there were concerns about similarities in the work.
Sources said there was a possibility that pupils co-operated with each other on projects, while others may have received unfair assistance from their teachers.
The Department said it had written to the schools concerned asking them about the issues involved.
It said schools and the candidates would be given every opportunity to respond to the issues raised.
"As is standard practice, the results for the candidates concerned are being withheld on a without prejudice basis until due process is complete," it said.
CSPE is made up of a written examination, worth 40 per cent of the marks, and an action project, which makes up the remainder. The Department said it was concerned only with the action project segment of CSPE.
The Department's guidelines say the action project must be "the candidate's individual work".
Last year there were also problems with CSPE at Junior Cert.
Yesterday Fine Gael criticised the Minister for Education, Mr Dempsey, over the matter. The party said Mr Dempsey had failed to clarify issues in relation to CSPE.
The party's deputy spokesman on education, Mr David Stanton, said: "There is serious confusion about the rules governing the action project part of CSPE.
"While students work in groups on their action project, they lose marks if their individual reports are similar to those of the rest of the group," he said.
"Nobody condones plagiarism but it is grossly unfair that schools are not notified in sufficient time to fully investigate cases before the results come out. This is not a new problem.
"It has been ongoing for a number of years, yet the Minister has not bothered to sort it out," he added.
Meanwhile, the Union of Secondary Students (USS) said it was unfair that some schools yesterday withheld results until late into the afternoon.
It said students should not have to wait hours for their results to be handed out.
The group's spokesman, Mr Daire Hickey, said the tension on results day was always high and schools should not be adding to it.
Some schools insist on releasing results late in the day to prevent students from organising drinks parties earlier in the day.