An International Baccalaureate examiner who plagiarised Wikipedia in a marking guide remained with the exam board for more than five weeks after it first became aware of the problem, The TES has learned.
In a statement, the International Baccalaureate Organisation (IBO) said the examiner had resigned last Friday, the day The TES revealed large chunks of plagiarism in the guide for marking a history paper sat by about 20,000 candidates.
In a letter to schools this week, Jeffrey Beard, IBO director general, wrote: "We have and always will take immediate and appropriate action when we discover any violation of our policies or standards."
But the letter also confirms that it was "late August" when "the IB became aware that a mark scheme associated with a history question paper contained plagiarised material".
Sent to the heads of more than 3,000 schools worldwide offering the IB, it says it "deeply regrets" the plagiarism. But it only mentions one marking guide. Last week the IBO told The TES it was also investigating two other guides where it has been suggested plagiarism took place.
There is no mention of the examiner's resignation in the letter. But it says: "The examiner concerned is no longer involved in writing question papers or mark schemes."
This is the second time in the past month that Mr Beard has had to write to IB schools about plagiarism in his exam board.
In the first, he had to explain his own embarrassing "oversight" when he plagiarised the work of another educationalist in a speech given to a US academic institution.
Reacting to Mr Beard's subsequent apology, one teacher wrote on The TES website: "The IB takes a firm stance on plagiarism and rightly so. When this happens, young people's academic dreams are dashed.
"They are given no opportunity to say, 'Oops, sorry!'"
An IBO spokeswoman said: "It was a voluntary resignation (by the examiner) at a time when they were not conducting any work for the IB."