Profits at England's only privatised exam board have risen seven-fold in three years, The TES can reveal.
One of Edexcel's directors earned pound;450,000 in pay and pensions contributions last year - easily the highest known figure earned by anyone in British education.
Edexcel's annual accounts for 2006 also show that it plans to revolutionise the way school subjects are taught and studied.
Since its takeover by the Pearson publishing group in 2003, Edexcel has moved from a yearly profit after tax of pound;3.6 million to the latest total of pound;25.1m on a pound;203m turnover.
The figures make it comfortably the most profitable of England's three awarding bodies and come as the board has moved from being a basket case to arguably the key player in the development of exams technology in just five years.
AQA, the largest board with twice as many GCSE entries as Edexcel, made pound;15.9m, while Cambridge Assessment, which runs the OCR board, made pound;5.7m, accounts for both boards for the year ending September 2006 show.
Edexcel's accounts recommend that pound;40m, equal to its profits for the past two years, is transferred from the company to its corporate parent, Pearson.
John Bangs, head of education at the National Union of Teachers, said of the profit figures: "This raises a big question as to who this money is for. Is it for a private company or is it for the good and quality of the examination system?"
Edexcel said: "Our success is because the qualifications we develop are well regarded and what our marketplace wants. Being commercial and profitable allows us to invest millions in education."
Edexcel has invested more than pound;80m in modernising its exams over the past three years and its business extends far beyond GCSEs and A-levels to Btecs, national vocational qualifications and key skills, it said.
Edexcel's nadir came in 2002 when ministers ordered the Qualifications and Curriculum Authority to send a troubleshooter into the board after exam paper blunders.
Since Pearson bought it, the controversy has continued. In 2005, a whistleblower told The TES that he and other unqualified employees had been asked to mark religious studies GCSE papers with only 20 minutes' training. But complaints have decreased.
The board has also been spearheading the move towards examiners marking GCSEs and A-levels at the computer screen.
Last week, Simon Lebus, group chief executive of Cambridge Assessment, said Pearson's takeover of Edexcel had been the biggest influence on the modernisation of the exams system.
He added that, given the risks involved with producing and marking exams, the profits made by any of the boards might be too low.
Edexcel said its plan to revolutionise teaching rested on two new products: Results Plus and eSpecs. Results Plus offers the chance for teachers and potentially pupils to get question-by-question analysis on how they performed in GCSEs. eSpecs are electronic, interactive versions of exam specifications.
The boards and their profits
Estimated share of GCSE market: 24%
Profits: pound;25.1 million
(Annual accounts for the year ending December 31, 2006)
Estimated share of GCSE market: 53%
Profits: pound;15.9 million
(Annual accounts for the year ending September 30, 2006)
Estimated share of GCSE market: 23%
Profits: pound;5.7 million
(Annual accounts for Cambridge Assessment for the year ending September 30, 2006. OCR is one of three boards run by Cambridge Assessment).