Some private schools may consider keeping children in Year 6 at home when schools reopen more widely despite the government's advice to prioritise the cohort, an independent school chief has suggested.
Christopher King, chief executive of the Independent Association of Prep Schools (Iaps), which has more than 600 members, said he expects the majority of members in England to reopen to more pupils from 1 June.
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Private schools have already begun making preparations for a wider reopening next month with one fee-paying school planning to use thermal cameras to detect whether children have a temperature.
It comes after teaching unions and council leaders have voiced concerns about the government's plans to allow children in nursery, Reception, Year 1 and Year 6 to return to school from next month.
Mr King said he is anticipating that the vast majority of prep schools in England will open and will "welcome the opportunity to get started again".
But he said that some private schools may decide to remain closed to Year 6 pupils who can continue their virtual learning at home.
He said: "It could be that a few schools decide that they won't open for Year 6 because there's so much confidence now in the way in which the online teaching is going, and not enough confidence that parents will want to send their children back in large enough numbers."
Mr King added: "Many prep schools, for example, offer subject specialist teaching by the time you get to Year 6.
"At the moment, online, the children will be getting that specialist education.
"The vast majority of schools are teaching a normal timetable with the specialist teacher in front of them, albeit remotely and virtually in that way.
"So the schools need to be confident that what they're going to offer will be superior to what they can do online."
He warned: "If you're asking teachers on top of that to perform two tricks at the same time, to deliver online and teach in the classroom, we may be asking just too much."
His remarks came as ministers were under growing pressure from councils, predominantly by Labour-run local authorities in the North of England, who oppose a wider reopening from next month.
Mr King warned that some private schools located in local authorities advising against a 1 June opening may have to remain closed next month – even if they wish to open.
"If a local authority were to say the school shouldn't open, it's going to be really difficult for the independent school to open so it may be forced on them anyway," he said.
But a large number of local authorities in England have said they will leave the decision on whether to reopen to individual headteachers.
And school leaders of private schools have begun planning for an opening in the first week of June.
Caroline Jordan, headmistress at Headington School, which has a prep school in Oxfordshire, will bring back children in Reception and Year 1 on 2 June and then Year 6 pupils on the following day.
The school, which has 250 children overall, will use electronic temperature checks and thermal cameras when children arrive, and it has installed new sinks outside for handwashing.
She said: "We believe that the children should be going back to school.
"We are very supportive of the government wanting to do that, as long as we have a very robust risk assessment in place."
When asked whether parents are concerned about sending their children back, Ms Jordan said: "We have a reasonable minority who say they are unsure at the moment, but I am confident that once they see the steps that we're taking they will be encouraged to send their children as well."
Geoff Barton, general secretary of the Association of School and College Leaders, said: "Like state schools, independent schools are doing their best to be ready to open more widely from 1 June, but are facing the same safety considerations, and we do know of a few which are planning a staggered start, with groups of children being phased in rather than all eligible pupils starting on 1 June."