More than 45,000 pupils will resit their English GCSEs next month after a scandal over grades.
About one in 14 who took the exam will resit, according to figures obtained by the BBC.
After complaints that the results had been downgraded students in England, Wales and Northern Ireland were given the opportunity to retake part or all of their exams.
The row over the English exams broke out as national GCSE results were published in August.
Ofqual, England's exams regulator, conducted an inquiry which concluded that January's GCSE English assessments were "graded generously" but the June boundaries were properly set and candidates' work properly graded.
A legal challenge over the fiasco is due to be submitted to the High Court in the next week, it was announced on Wednesday.
The unprecedented action is being brought by an alliance of pupils, schools, councils and professional bodies, angry at decisions which meant thousands of teenagers missed out on C grades.
A spokesman for the alliance said that following a meeting of legal representatives, it was decided that a claim for a judicial review will be put forward.
"We have now thoroughly examined the case that we have and we are convinced of the merits of our case, and the expectation that we will have a success to get the outcome we want - which is a regrade for students," he said.
"We will be putting our claim together and submitting it over the next week."
Last week Ofqual responded to a pre-action letter sent by the alliance, vowing to "rigorously defend" its decisions over this summer's English results.
The letter, sent to the AQA and Edexcel exam boards as well as Ofqual three weeks ago, set out plans for legal action over decisions by the boards to increase the boundary for a grade C in GCSE English between January and June.
It also proposed taking action against what they claim was a failure by Ofqual to address the situation.
Ofqual responded two weeks later with a spokesman saying the regulator was "rigorously defending our decisions".
"Our work to understand why some schools' results differed significantly from their expectations is continuing and we will report again shortly," he added.
Brian Lightman, general secretary of the Association of School and College Leaders (ASCL), which is part of the alliance, today said: "We are very disappointed that Ofqual and the awarding bodies have refused to take responsibility for their actions and to acknowledge that many thousands of young people's career ambitions have been undermined by a failure to implement the new qualification properly."
In Wales, education minister Leighton Andrews ordered the WJEC exam board to regrade Welsh students' English papers.
As a result, last month nearly 2,400 pupils who took English with the exam board received better results after a review of the marking system.