More than 10,000 teenagers were due to see their A-level mistakes yesterday as part of a pilot scheme to allow pupils and teachers to scrutinise marked papers.
Photocopies of A-level scripts were returned to 1,000 schools and colleges in England and Wales as part of a project to help pupils and teachers learn from their mistakes and reduce exam appeals.
Pupils who studied any of 10 selected A-level syllabuses will be able to see copies of their marked papers, including examiners' comments.
All pupils in the pilot have had to sign a confidentiality agreement promising not to show their marked papers to anyone but their parents and teachers.
The QCA is also piloting different ways of allowing GCSE candidates to see their marked scripts. Some students will be free to take their scripts away, others will only be shown the papers under "controlled" conditions.
Later this month, pupils at 200 schools will have all their scripts returned. Schools are due to receive GCSE results next Thursday, but the scripts will not be available for viewing until the following Tuesday because of sheer volume of papers to be returned.
Exam boards say the pilot should not change the way examiners mark the scripts. However, boards have written to examiners reminding them that parents, teachers and pupils may see the papers and reminding them not to add "inappropriate" comments.
The QCA will assess the different pilots to see which was the most effective and cost-efficient.
In New Zealand, where all scripts are returned, and in Ireland where a similar system has run for one year, there had been a drop in appeals, officials said.
Last year, schools and colleges raised 14,923 queries on A-levels with exam boards involving 29,129 candidates - or just 0.5 per cent of all entries. Boards agreed to change grades in 9 per cent of these cases. At GCSE, schools and colleges raised 10,991 queries, covering 17,800 candidates, or 2.3 per cent of all entries. Grades were changed in 9 per cent of cases.