The Oxford and Cambridge exam board OCR and the London board Edexcel have been told to improve after they failed to meet targets for dealing with complaints and re-marking scripts.
The first-ever league table of exam board performance, published this week by the Qualifications and Curriculum Authority, revealed that the two boards had failed to meet challenging targets for tackling complaints about last summer's exams.
The QCA had demanded that all urgent queries - especially those where a university place was at risk - be dealt with within 30 days and all others be settled within 40 days.
However, less than 55 per cent of OCR's fast-track A-level re-marking was completed on time compared to 65 per cent of Edexcel's.
Only the Welsh and Northern Ireland boards, WJEC and CCEA, which have far fewer candidates, managed to hit te priority targets.
Tthe Assessment and Qualifications Alliance, which has by far the most A-level entries, failed to reach its demanding target but was praised for dealing with nearly 3,000 re-marks within 30 days. AQA dealt with 97 per cent of fast-track complaints on time.
A-level candidates of the Northern Ireland board were most likely to receive the wrong grade the first time round, with one in 164 needing an upgrade.
Edexcel was marginally better with one in 172 students upgraded, followed by AQA's one in 208. WJEC had the most accurate marking, closely followed by OCR where only one in 370 candidates needed an upgrade.
Just under 3,000 GCSE papers were upgraded last summer after 10,343 complaints from schools concerning 26,371 candidates - out of a total of more than 5.7 million entries. At A-level, just under 3,500 candidates received an upgrade after 22,983 complaints - out of nearly 790,000 entries.