Tanya Osbourne wrote to Ruth Kelly, the Education Secretary, two months ago complaining about Edexcel and has vowed never to let her pupils take its exams.
The 23-year-old was sent maths instead of religious studies papers to mark after she made repeated complaints about faults with the marking software.
Last year the fully trained teacher and examiner found GCSE scripts had been dumped in the garden by a courier. "I would never let my pupils sit Edexcel exams," she said. "The way they have handled these matters has been completely inadequate."
Last week The TES revealed how an unqualified member of Edexcel's staff marked extended writing sections of the religious studies exam after 20 minutes' training. Richard Pope, pictured left, has now resigned. He is to train as a teacher and said he was shocked at the potential for haphazard marking. "These issues could affect pupils I will be teaching in two years'
Edexcel said it remained confident about marking procedures.
The Department for Education and Skills said it had replied to Ms Osbourne's letter but could not comment on her complaints.
The National Union of Teachers has called for an inquiry but the Qualifications and Curriculum Authority said it had no plans to investigate.
David Cameron, Conservative education spokesman, said: "Examples like this will continue unless the QCA begins to properly marshall the process."