Clive Sheldon QC, representing an alliance of of pupils and schools, local councils and teaching unions in a legal action, told two judges it was not the fault of the students who had been awarded lower than expected grades in this summer's GCSE English exams.
He said the students had "worked well and hard" and added that the evidence of unfairness was overwhelming. Mr Sheldon said the students were the victims of a radical change in grade boundaries that occurred without warning.
He said Ofqual had given an instruction to avoid "grade inflation", and bodies awarding grades were required to meet tolerances set by Ofqual based on statistical predictions derived from students' performances in Key Stage 2 examinations five years previously.
More top news
Oscars 2017: Watch the Academy Awards nominations live
Hull City midfielder Ryan Mason is making "excellent progress" after suffering a fractured skull at Chelsea.
HSBC is to close 62 branches across the UK in 2017, the bank said.