The credibility of the International Baccalaureate (IB) has been badly undermined, as it emerged that it has plagiarised large chunks of its marking guides from Wikipedia.
One of the confidential mark schemes, which provide examiners with model answers to help them grade papers, was for a history paper sat by about 20,000 candidates worldwide this May.
An IB examiner who spoke to The TES in England said they were "shocked" to discover there were "serious examples of academic dishonesty", throughout the document, with guides for 14 of the 24 questions containing large sections copied wholesale from unattributed websites, including Wikipedia.
The TES has learnt that the mark scheme is one of at least three being urgently investigated by the International Baccalaureate Organisation (IBO) over plagiarism allegations.
The news follows last month's public naming and shaming of Jeffrey Beard, IBO director general, for plagiarising the work of another educationalist in a speech without acknowledging his source.
This week the IBO admitted that using Wikipedia, an online encyclopaedia to which anyone can contribute, was not "acceptable practice".
Wiki contributions "cannot be guaranteed because the sources are uncited", an IBO spokeswoman said. A pupil who copied their exam answers or coursework from Wikipedia would be found guilty of malpractice and would not receive a grade, she added.
The examiner who uncovered the marking guide plagiarism said they were "embarrassed" for the IBO.
"It will be difficult for me to insist that my students practise academic honesty when the very organisation which creates examinations and then assesses them according to often uncited materials does not follow these same guidelines," they said.
Another teacher who runs training workshops for the IBO said they were "livid" and "stunned" and that the whole IB programme had been put at risk.
Increasing numbers of schools in England have been turning to the IB as an alternative to A-levels. Only a handful of institutions offer it in Scotland, including the private St Leonards School in St Andrews and Motherwell College.