Rank-ordering exams students could amount to a "rationing of grades" based on previous performance, teachers have warned.
Exams regulator Ofqual announced today that GCSE and A-level grades calculated by schools will be checked using a rank order of students.
It said this will be used in the "statistical standardisation of centres’ judgements" – allowing "fine tuning" of the standard applied across all schools.
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But the NEU teaching union has said that, while moderation by the regulator helps with "consistency and fairness", many teachers will be "uncomfortable" with the process.
Mary Bousted, NEU joint general secretary, said it could amount to "rationing" grades.
"Many teachers will be uncomfortable with the concept of rank-ordering students, especially if it amounts to a rationing of grades based on previous performance data," she said.
"Moderation does not have to mean rank-ordering students nor rationing of success and in an ideal use of teacher judgements during awarding, this would be possible.
"This crisis demonstrates again that England’s high-stakes exams-based system is not resilient.
"In other nations of the UK, awarding is being assisted by the fact that not all of the assessment was left until exams at the end of the course.
"We hope the work done here can open up a longer-term conversation about the impact on our pupils of unnecessary high-stakes exams."
Ofqual will ask schools to provide a rank order of students by performance for each grade, which will be used to "standardise judgements".
This means that if a school were to award a generous proportion of grade 6 in history, for example – a legacy high grade B – it would be possible for boards to moderate on the basis of its rank order for that grade.
The rank order would include the pupils who were most secure in their attainment of grade 6 down to those who were least secure in attaining the grade.
Paul Whiteman, general secretary of the NAHT school leaders' union, said schools "must not share" the rank order with students or their families before final results have been issued.
"This will help to protect the integrity of teachers’ judgements," he said.
"Since the grades students are finally awarded by the examining body could be different from those submitted, this will also help to avoid confusion."