Summer vacation may have to be canceled for some students, said a former Ofsted chief inspector.
Sir Michael Wilshaw warned that age groups about to take exams may have to make up for lost time during the summer holidays.
Thursday, the decision to reopen schools is widely expected.
The Ministry of Education (DfE) said there were no plans to cancel the vacation and a teachers’ union said the idea was “not realistic”.
As part of the government’s roadmap to lift the closure, schools can start reopening from June 1 – but it will depend on the rate of spread of the virus – the R number – which will remain low.
Prime Minister Boris Johnson announced the plan for England on May 10 and said primary schools would be reopened as part of the second wave of closings, but only for those in reception in grades one and six .
Speaking on Sky’s Sophy Ridge show on Sunday, Sir Michael said that some children, including the poorest, “regressed” during the lockout.
“It is a great shame because we want each group of the year to have the same opportunities as the others,” he said, adding that it is the responsibility of schools and principals when the lockdown ends. to set up recovery programs, which could mean vacation cancellation.
He warned of “a lost generation of young people”.
“We will wait and see,” he said. “What is absolutely clear is that a lot of young people lost a lot of time during this lockdown. “
A spokesman for the DfE said: “The Secretary of Education said that we do not plan to run schools during the summer. “
“But we are working with partners to explore additional measures that may be necessary to ensure that every child has the support they need to cope with the impact of the coronavirus on their education. “
Geoff Barton, secretary general of the Association of School and College Leaders, said: “The idea of opening schools and colleges during the summer holidays does not seem realistic. “
He added: “We should also be aware that many teachers have worked hard on distance learning, managed emergency services in schools and sorted the grades assessed by the center for students whose pupils GCSE and A-level exams have been canceled. “
Other nations have established their own policies, with Scotland and Northern Ireland only reopening schools in August at the earliest.
The Welsh government has said it will not reopen schools on June 1 – although it has not set its own timetable – and Prime Minister Mark Drakeford has criticized the government’s preparations.
Unions and educational boards have expressed concerns about the safety of students and staff in the event of school reopening.
Sir Michael said that, when it was time to reopen schools, it was “essential” for parents to be convinced that it was safe to do so.
“It’s good to open schools but if the parents lack confidence, they will not send [children] ” , he said.
He also described social distancing for five-year-olds as “like herding cats”.
While parents will be “strongly encouraged” to send their children to school, unless a member of the household is part of the protected group, fines for unauthorized absence will not be reintroduced on June 1, said the DfE.