Ofqual chief regulator Glenys Stacey has said "children have been let down" by school exam systems and that she was "shocked" by the findings of the report.
We have been shocked by what we have found. Children have been let down. That won't do.
It's clear that children are increasingly spending too much time jumping through hoops rather than learning the real skills they need in life. That won't do.
Teachers feel under enormous pressure in English, more than in any other subject, and we have seen that too often, this is pushing them to the limit. That won't do either.
Headteachers have said that tens of thousands of teenagers received lower GCSE English grades than expected this year after exam boards moved the grade boundaries between January and June.
An initial report by Ofqual concluded that some of January's assessments were "graded generously" but the June boundaries were properly set and candidates' work properly graded.
The regulator today published its second report, looking at the reasons behind the changes in results.
More top news
Former Girls Aloud singer Kimberley Walsh is pregnant with her second child, she has revealed.
Chancellor George Osborne will seek to reassure financial markets on Monday morning following Britain's decision to leave the EU.
In his first outing since the referendum result, the lead Leave campaigner has outlined his vision for a post-Brexit Britain.