Schools across the country are having to close or partially close as they struggle to cope with staff shortages from teachers self-isolating due to coronavirus.
The moves follow prime minister Boris Johnson's announcement on Monday of stricter measures aimed at "social distancing".
Those measures stopped short of closing schools, but many headteachers say they have been left with no choice but to shut, or operate at limited capacity, due to the number of staff now self-isolating.
At Stretford High School in Manchester, students have been told to stay at home for their own safety.
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In a written message, headteacher Nicola Doward said the school would be closed until 14 April.
She wrote: "The impact that this advice has on [our] staffing means it is not operationally possible to run the school safely. We find ourselves in this situation because we cannot follow all of the government’s advice AND keep our children and our Stretford families safe."
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It was "unacceptable", she said, that staff members were not being tested for the virus. "This would have allowed me to either keep the school open or to be able to identify who, if anyone, is at risk," she said.
She did not feel comfortable combining classes into larger groups, as this could exacerbate the spread of the virus.
Other schools are staggering days of absence, with different year groups asked to remain home on different days of the week.
Saint Joseph's Catholic School, in Salisbury, Wiltshire, is operating at "limited capacity". A note on the school's website says that today, pupils in Years 7 and 11 should attend school but not Years 8, 9 or 10 "unless this would cause significant issues around safety or parents' work for emergency services/NHS".
Ralph Allen School, in Bath, has closed to all but Year 11s and 13s because of "falling staff numbers, due to self-isolation for symptoms, or those who are risk from the coronavirus", according to a note on its website.
Tes is aware of many other schools taking similar decisions.
Yesterday, the Association of School and College Leaders union warned that up to one in five teachers were self-isolating.
In London, several schools have closed for the week. The London Oratory School in Fulham, south-west London, closed yesterday after its second confirmed case of someone in the school contracting Covid-19.
Yesterday, chief medical officer Professor Chris Whitty said that schools across the country would only close "at the right time, in the right way and at the right stage of the outbreak".
However, the Department for Education said for the first time that some schools might need to close if they faced "operational" difficulties as staff self-isolated.