Edexcel has been identified as the exam board with the worst customer service, based on this summer's GCSEs and A-levels.
Out of 288 schools and colleges that took part in the Ofqual survey, more than 90 per cent needed to contact an awarding body by telephone before or during the exam period. This was a positive experience for 79 per cent of those contacting the AQA and 52 per cent calling OCR but only 36 per cent of those contacting Edexcel.
It was "not at all easy" to get through to someone who could help for 16 per cent contacting Edexcel, but for only 1 per cent calling AQA and 6 per cent of OCR users. Ofqual recommended that awarding bodies set up dedicated exam telephone lines to help schools contact a relevant person who could help them promptly.
Ofqual said the most common issues raised concerned entries, access arrangements or missing exam papers.
An Edexcel spokeswoman said the findings were "disappointing", adding: "We do not feel this is a fair reflection of the situation as it has not taken account of additional evidence available to the QCA."
Edexcel is considering extending subject-specific advice and support services, she said, and will provide named subject advisors in more than a dozen qualification areas.