Teenagers have been let down by an exams system that is abused by teachers who are under intense pressure to achieve good grades, Ofqual has warned.
Teachers in some of England's secondary schools were guilty of "significantly" over-marking pupils' GCSE English work this summer in order to boost results, according to chief regulator Glenys Stacey.
In a new report into the GCSE English fiasco, Ms Stacey said that it is hard for teachers to maintain their integrity when they believe that others are abusing the system.
She laid blame for the debacle on intense pressure on schools to reach certain targets, which led to over-marking, as well as poorly designed exams and too much of an emphasis on work marked by teachers.
Ms Stacey said: "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 published its second report, looking at the reasons behind the changes in results.
An alliance of pupils, schools, councils and professional bodies have launched a legal challenge over the fiasco, calling for this summer's English results to be re-graded.
ASCL deputy general secretary Malcolm Trobe said: "For Ofqual to suggest that teachers and schools are to blame is outrageous, and flies in the face of the evidence. Ofqual is responsible for ensuring fairness and accuracy in the system. The fact remains that different standards were applied to the exams in June and January and this is blatantly wrong."
Christine Blower, general secretary of the National Union of Teachers, said: "Ofqual seem to be shifting the blame whilst at the same time exposing the nonsense of floor targets. They continue to refuse to acknowledge the mistakes they have clearly made. It is high time Ofqual took some responsibility for a situation of their own making. The solution is to regrade the exams of young people who, together with their teachers, worked to the parameters set in January."