Though the Independent Schools Council (ISC), which represents more than 1,300 independent schools in the UK, said it was seeking “urgent clarification” from the government over its plans.
Julie Robinson, ISC chief executive, said: “All schools put safety first and are concerned for their communities. Independent schools share the concerns expressed by the unions today.”
Dr Mike Tildesley, a University of Warwick epidemiologist who advises the government as part of the Scientific Advisory Group for Emergencies (Sage), said that while there was a rise in cases in secondary school age groups, there was not strong evidence of transmission in the school environment.
The National Education Union (NEU), which is the UK’s largest education union and has more than 450,000 members, said all primary and secondary schools should remain closed for a further two weeks after the school holiday.
It is advising members against working in school.
The National Association of Head Teachers (NAHT) called for all schools to move to home learning for a “brief and determined period for most children”, and said it would issue guidance to head teachers recommending they take no action against staff who refused to return to work if they felt unsafe.
And in a letter to the education secretary, the NASUWT called for an “immediate nationwide move to remote education” as the “only sensible and credible option” to minimise risk, while the GMB, which represents support staff, called on Mr Williamson to apply “common sense”.
Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said the government’s plans for the start of the spring term were “untenable”, adding that face-to-face teaching should be restricted to only vulnerable children and those of key workers until at least January 18.
The ASCL and the NAHT have started legal action to get the Department for Education to share any information showing “why they think it is safe to reopen schools on Monday, given the higher transmissibility of the new Covid-19 variant”.
Pressure is growing on the government to keep all schools in England closed for two weeks after the Christmas break amid a surge in coronavirus cases.
Teaching unions have told primary school staff it is unsafe to return to work, and called for remote learning.
Head teachers have begun legal action to force ministers to reveal data behind the decision for some schools to reopen on Monday.
The government said decisions are based on new infections and NHS pressure.
Labour has accused the government of “creating chaos” for parents.
Most primary schools in England are expected to open on Monday while secondary schools will reopen on a staggered basis, with exam year pupils returning on 11 January and others returning a week later.
On Friday, Education Secretary Gavin Williamson announced that all of London’s primaries would remain shut on Monday – reversing a decision to keep only schools in certain boroughs closed.
He said the closures were a last resort in the face of a fast-moving situation.
Elsewhere, Brighton and Hove Council has advised primary schools to switch to remote learning next week.
Meanwhile, president of the Royal College of Physicians, Prof Andrew Goddard, told the BBC the new highly infectious strain of coronavirus was spreading across the country, adding: “All hospitals that haven’t had the big pressures that they’ve had in the South East, London and south Wales should expect that it’s going to come their way.”