Examiner found scripts lying in garden
Ms Osbourne, who teaches religious studies at a secondary school in St Albans, marked around 950 GCSE scripts in her subject for the exam board last year.
The 23-year-old said she had been concerned about the security of exam scripts last summer when she found a package of them in the garden of her parents' house in the small Hertfordshire town of Radlett, where she was living.
"I kept wondering what would have happened if they didn't live in such an all-right area," she said. "Someone could have walked off with them."
The incident was not enough to deter Ms Osbourne, though, from agreeing to mark religious studies papers for Edexcel again this year.
This time, the board asked her to use its electronic "e-pen" system, in which scripts are scanned in electronically, then marked on computers. But she had difficulty getting the programme to work on her computer at home and said that the board's IT support was "unhelpful and rude".
When the programme was finally running, she found that Edexcel had sent her maths GCSE scripts electronically instead of those for the religious studies exam.
In frustration, she quit the project in June and wrote letters about the mistakes to Edexcel as well as to Ruth Kelly, the Education Secretary, and David Cameron, Conservative education spokesman.
"I would never let my pupils sit Edexcel exams," she said. "The way they have handled these matters has been completely inadequate."
Although she is critical of the company, Ms Osbourne praised Dave Ansell and Victor Watton, Edexcel's co-ordinators of the religious studies exam, saying they were working hard in difficult circumstances.
She said she had been appalled to read in The TES last week about unqualified staff being used to mark extended writing papers.
As a religious studies teacher, she said she recognised that the questions were of such complexity that they needed a marker with specialist knowledge.
"There is a reason why Edexcel is having a problem getting RS markers when you don't hear of it happening at (the other boards) OCR and AQA," she said.
Edexcel said it had received and replied to the complaints from Ms Osbourne.
A spokesman said that the maths papers had been sent to her as a test to see if her system was working. "She was not expected to mark them, but, unfortunately that may have not been made clear to her," he said.
Edexcel added that it was "regrettable" she was unhappy with the support she had received from the company, as 90 per cent of markers were satisfied with the help they received.
The spokesman said the company instructed its couriers to get signatures when delivering exam scripts but that this did not occur in some rare cases. "They certainly should not be left in a garden," he said.
Carol Adams, chief executive of England's General Teaching Council, said she shared Ms Osbourne's concern about the use of unqualified markers.
"Students are entitled to expect their efforts to be judged by someone with appropriate professional knowledge and training," she said. "Their teachers expect the same for them. Anything less risks undermining further public confidence in the examination system."