Headteachers have raised concerns over a possible lack of invigilators and markers for GCSE and A-level exams in 2021.
Speaking to Tes, Geoff Barton, general secretary of the Association of School and College Leaders, said: "I suspect awarding organisations are already worried about whether we are going to have all the markers needed in the summer.
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"School leaders have been saying to us, we don’t think we’re going to get the invigilators as, because a lot of invigilators are retirees, will they want to be in school?
"So you can see how many different elements are in the mix in trying to run exams as normal next summer."
The news is the latest in a number of concerns over how exams will take place in 2021, amid uncertainty over whether the pandemic will allow for a full suite of GCSEs and A levels next summer, as well as how they will be modified to avoid penalising students.
Last week, it was revealed that England's chief exams regulator thinks the grading in 2021 should be more generous to take the "baleful" influence of the coronavirus on education into account.
And yesterday, following the Welsh decision to cancel next summer's exams, the Department for Education insisted they would happen in England.
However, some have raised doubts over whether exams can go ahead in the event of a further wave of Covid-19.
Barnaby Lenon, a former Ofqual board member and head of the Independent Schools Council, said last week that GCSEs and A levels would need to be cancelled during a "third wave" of the coronavirus.
He said that in the event that it was "too dangerous" to hold exams, centre-assessed grades and rank orders of pupils would need to be used, as in 2020 – and that the government would not use an algorithm to determine grades again.
Ofqual has said that it will need to make exams "less daunting" in order not to penalise students who have missed out on learning time this year.
A spokesperson for the Joint Council for Qualifications, the body representing England's school exam boards, said: "JCQ and the exam boards are continuing to work with, and will need the support of, the DfE, Ofqual and the exam sector to recruit the invigilators and thousands of extra examiners required to safely conduct the summer 2021 exam series.
"We recognise and thank examiners for their crucial work year in, year out.
"With more than 25 million exam scripts needing to be marked annually, there are significant opportunities for subject specialists interested in becoming an examiner.
"As in any examination year, it gives teachers a valuable insight into the assessment process, networking opportunities and career development.
"We welcome Gavin Williamson’s earlier request that Ofqual work with him, schools and further education leaders, unions and the higher education sector to develop arrangements for recruiting extra examiners. We recognise the challenges exam centres are facing in an ever-evolving set of circumstances related to Covid, along with the need to recruit the invigilators required for the forthcoming summer exam series."