More than 45,000 pupils - around one in 14 students in England, Wales and Northern Ireland - will resit their English GCSE exams next month as a result of the row over this summer's grade boundaries.
Headteachers said it was a "gross injustice" that students will have to do resits after a scandal that was not their fault.
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Every school rated as inadequate by Ofsted will be turned into academies under new laws, the Education Secretary has announced.