Pupils at a school for youngsters with additional needs had to return exam certificates after a mix-up in their results.
Falkirk Council has launched an internal investigation over the incident which affected those who sat exams in May 2017.
However, it is understood that the Scottish Qualification Authority (SQA) is also investigating both Carrongrange School and the education authority for “malpractice”.
Around 70 per cent of pupils who sat the SQA papers are believed to have been affected.
Now parents and relatives are demanding answers from the council over how this occurred.
Pupils who received their certificates last August were given a letter by head teacher Gillian Robertson shortly before last Christmas asking them to return them.
However, there was no explanation over why they had to be returned.
It wasn’t until after the Easter holidays that youngsters were given the corrected certificates.
On the original paperwork some teenagers at the school had received awards in subjects they had not sat while others had the correct subject but the wrong level.
One concerned relative said: “It seems to have been a complete mess. We’ve been told informally that something like 70 per cent of the pupils presented by Carrongrange had at least one mistake in their certificates.”
Another source said: “There is no doubt that there was a major failure in 2017 and as a result something like two thirds of the SQA certificates awarded to Carrongrange students were wrong because the information sent by the school to the SQA was wrong.”
They alleged that teachers at the school warned managers both within the school and at education service headquarters that the wrong information was being sent but they were ignored.
A spokesman for Falkirk Council said: “An administrative error occurred last summer at Carrongrange School, which resulted in a number of pupils being issued with incorrect SQA certificates last year.
“As soon as the error was identified we acted quickly and worked with the SQA to rectify the situation. The pupils affected have had their certificates corrected to accurately reflect their work and qualifications passed.
“A full review of systems and processes has also been completed and we offer our apologies for the confusion this error caused. No pupils will be disadvantaged by this situation.”
A spokesperson for the SQA would only say: “If a malpractice investigation is initiated, schools and local authorities are informed and involved in the process. The findings and the action plan that follows remain a matter between the SQA, the school and the local authority.”
Margaret Smith of the teaching union the EIS said: “We are aware of the ongoing investigation.”
Carrongrange School opened in its current site in Grangemouth in August last year having transferred from the previous building in Larbert and can accommodate around 190 pupils.
Built at a cost of £17.5 million, the project was led by hub East Central Scotland in partnership with Falkirk Council, Scottish Futures Trust and Ogilvie Construction.