When teacher Andrew Roberts, not his real name, wanted to raise pupils' standards at GCSE, he turned to a course run by an independent educational training company.
"The syllabus we had from the exam board was scarily vague... it didn't tell you what to do. So we thought, we'll go along and find out what's going on... and they told us how to pass the exam," he said.
Mr Roberts found the course, in November 2006, effective. It wasn't run by the AQA examination board, who designed the GCSE his students were studying, but by a second company called, Keynote.
Mr Roberts was surprised that among the speakers, was an examiner.
He added: "It's a way to work the system a little bit. I think that's why you pay for it. If you talk to the person that's setting it, they won't tell you exactly what will be in the exam but they can tell you to have a look at this, that or the other."
A Keynote spokesman denied any improper behaviour by its course tutors.
He said: "We adhere to the stringent regulations set by each examination board. We can guarantee that none of a courses would overstep the mark and give teachers an unfair advantage."
On its website, Keynote advertises courses taught by examiners from some of England's chief exam boards, although none of the courses advertised feature examiners from the AQA board.
Mr Roberts says he attended several courses with various companies during his six years as a teacher.
"Some were a bit nudge, nudge, wink, wink. Others were absolutely blatant, telling you what areas would come up," he said.
Sometimes there was even guidance on the specific wording students should use in their answers.
He said tutors at the courses he attended would be fairly open about standards.
"They would tell us things like if a question ended up with too many candidates getting it wrong they would just take it out and wouldn't ask it on future papers."
A statement from AQA said: "AQA's senior examiners are self-employed and AQA has no legal right to prohibit them from undertaking work for other organisations. What we can and do prohibit is their using their AQA position for commercial gain.
"Examiners must not make use of their association with AQA for commercial purposes, eg by identifying themselves as AQA examiners in books or on the internet or in advertising tutorial services or involvement in courses organised outside of AQA."
Examinations regulators, Ofqual, are planning to investigate potential conflicts of interest in the sector, particularly in relation to study aids such as text books and training services.
In a letter written to the schools minister, Nick Gibb, last month, the Ofqual chief executive Glenys Stacey said she wanted to develop a long term action plan to address the issue.
Mr Roberts left teaching last year and is now retraining as a commercial pilot.
'Rock the boat'
He said the career change was was partly prompted by disillusionment and a perception that what he sees as a corrupt exam system is leading to lower standards in schools.
He believes that pressure on schools for top results is leading them to seek out exam boards that give the greatest number of top grades.
He says the boards are complicit in lowering standards because of competition between them for business.
Mr Roberts said he has himself worked as an examiner with another board. He said that he has evidence of duplication in some of the course work he moderated that could indicate that students copied from one another or were handed a draft text by a teacher.
He said that when he pointed this out to his line manager he was told to ignore it.
"I have been moderating for five years. In previous years we'd have raised it and put it through the proper procedures and chased it up. This time the instruction was 'pretend you haven't seen it, don't rock the boat'.
Mr Roberts believes one solution could be to go to a single examination board but he thinks that is unlikely to happen.