'Shambles' of administration
He quit after spending nine days trying to get the Assessment and Qualifications Alliance to tell him whether it would send him 100 extra scripts to mark.
"This has been a complete cock-up, right from the word go," he said. He has vowed not to mark scripts for the board again.
Problems began for the 56-year-old in March when he realised he had received no notification from the AQA of this year's marking arrangements, despite telling the board he was available.
After the exam board eventually found his records, he marked a "basic allocation" of 451 English literature higher tier scripts, and then an extra 240, and posted them all off as normal.
On July 8 he offered to take a further 100 scripts. Four days later, he rang to ask whether the scripts were on the way and was told he would be called back. Three days later, still waiting for the call, he rang again.
Two days after that, there was still no response from AQA, and he wrote to resign.
The board has now written to Mr Barrett, who teaches at a private school in Croydon, south London, offering "profuse" apologies.
It wrote: "It is a matter of regret that the requests were not immediately followed up and that you were not actually sent any scripts. I fully appreciate your exasperation at the number of times you had to telephone AQA."
An AQA spokesman said: "This is one examiner out of 27,000 working for the AQA, but nevertheless that is one too many.
"He should not have been put in this position."
Examiners are supposed to be paid within 31 days but Mr Barrett said he had not been paid the pound;2,000 owed, 43 days after finishing the work.
Mr Barrett said he had rung the board repeatedly to check where the money was, to be told it was about to be posted. He is now considering taking out an overdraft to pay for a holiday.