Headteachers have said it is a "gross injustice" that tens of thousands of students will have to resit GCSE English next month after a scandal that was not their fault.
Around one in 14 students - more than 45,000 in total - who took the qualification in the summer have opted to retake exams, according to figures obtained by the BBC.
One school leaders' union said the numbers were "higher than expected", and warned that offering students an extra chance to resit was not the answer to the ongoing GCSE English fiasco.
The figures came as an alliance of schools, pupils, professional bodies and councils announced they will submit a legal challenge over the debacle to the High Court in the next week.
Thousands of students received lower than expected results in GCSE English in the summer after grade boundaries were raised between the January and June exam sessions. Following an investigation by exams regulator Ofqual, students in England, Wales and Northern Ireland were offered the chance to resit all or part of the course.
But headteachers say pupils who were affected should not have to resit as the problems were not of their making, and are calling for this summer's GCSE English papers to be regraded.
Brian Lightman, general secretary of the Association of School and College Leaders (ASCL), said: "We've said all along this is not the solution, because if the exams are graded in the same way as they were in the summer then students will still find their results are down. What this shows is that it is a gross injustice that this vast number of students are being subjected to go through a resit when the fact is this is not their fault."
He added that the numbers retaking all, or part of the course, are "higher than expected, and shows the extent of the problem".
Figures from four exam boards, AQA, Edexcel, OCR and WJEC, show that over 45,000 candidates have opted to take part in the November resit. Of these, the majority, around 32,000, are candidates with the AQA board. This is because AQA has a high number of GCSE English students, with 380,000 sitting the qualification in the summer.
Both OCR and Edexcel each have around 4,300 candidates taking part in the resit, and WJEC, the Welsh exam board, has around 4,700.
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