The Edexcel exam board has set up marking centres in the American mid-west and Sydney, Australia, to assess answers in eight subjects.
Papers are being scanned electronically. Tick-box and short answers are sent to the two overseas centres and one in central London to be processed by markers who need not be teachers. Longer responses are sent to British examiners.
Edexcel said the move, part of a trial of electronic marking in all GCSE subjects, will speed up the grading process without compromising standards.
It said the change offered round-the-clock marking, because the centres operate in different time zones.
But the move, approved by England's exams regulator, will add to controversy surrounding the privately-owned Edexcel, which became a profit-making organisation last year.
One chemistry GCSE marker said: "I would not want my child having their paper marked by someone who is outside the British education system."
The subjects covered are GCSE science, information and communication technology, maths, languages and music. Also included were general national vocational qualifications in health and social care, ICT and business.
Edexcel is employing 125 staff in Iowa and Sydney, and 100 in London, to carry out the fill-in-the-box-type marking. It said the overseas staff have been extensively trained and are being paid more than British counterparts.
Frank Wingate, head of media affairs, said: "This will help make the marking system more efficient while easing the burden on our markers in the UK."
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