Ofqual review of GCSE English grade claims angers heads
Head teachers have been left angered by the refusal of exam regulator Ofqual to order exam boards to regrade this summer's GCSEs in English.
On Friday the body for England acknowledged grade boundaries had changed between January and June but offered only resits to affected pupils.
One head teachers' union said there had been a "systemic failure" and it was still considering legal action.
Labour is planning to raise the issue in the House of Commons on Monday.
Teaching unions are angered that many pupils now face the prospect of resitting exams rather than having their papers automatically regraded.
They claim those who sat the exam in June were at a disadvantage, compared with those who had sat English GCSE earlier in the year, because the summer's exams were marked over-harshly after Ofqual had told exam boards to keep an eye on grade inflation.
Head teachers' union the Association of School and College Leaders (ASCL), which had urged Ofqual to investigate, said it was still considering a legal challenge on the issue.
Many pupils who had been expecting a crucial C grade were given a D as a result of the grade boundary changes. This means some will be denied college places.
ASCL general secretary Brian Lightman said there had been "a systemic failure over the awarding of English GCSE grades".
He added: "Teachers and students acted in good faith, followed advice and feedback from the awarding bodies during the year, and worked to the approximate grade boundaries given to them.
"They accept that grade boundaries can change by a couple of marks, but to change by 10 or more makes a mockery of the system."
Russell Hobby, general secretary of the National Association of Head Teachers, said "the gravity of this situation cannot be overestimated".
After carrying out a review into the issues first raised last week, Ofqual chief executive Glenys Stacey said on Friday that it had found that the June boundaries had been properly set and the problem rested with the January standards.
However she said the papers had been fairly marked, and pupils could resit the exams early.
Ms Stacey said examiners had used their best judgement in setting grade boundaries at all times, but those marking in January - when just 7% of candidates had sat the unit causing concern - had had less data and information to work with.
Labour said Ofqual had not addressed the situation of students in the same year, who received the same marks, being awarded different grades.
BBC political correspondent Iain Watson says the report from Ofqual appears to have exacerbated rather than quelled the row.
Education Secretary Michael Gove will be questioned by MPs on Monday and Labour will be pressing him to say whether he believes it is fair for pupils to have to resit exams for reasons beyond their control, our correspondent adds.
Labour is also pushing for the cross-party education committee to conduct an inquiry. A decision will be taken on Wednesday.
Our correspondent says Mr Gove will be pleased that Ofqual exonerated him of the charge of political interference in the exam results.
The education secretary is now expected to go on the front foot, arguing that the current row underlines the need for a radical overhaul of the exam system in England, he adds.
Overall, this year's GCSE results showed the first fall in the proportion of A* to C grades since the exams were introduced.