Bringing all pupils back to class could fuel the pandemic and put teachers at "serious risk" of falling ill, a coalition of education unions has warned.
The Government's "chaotic" handling of the opening of schools has caused confusion for parents and teachers, according to a joint statement from unions representing school staff and headteachers.
All of London's primary schools and those in some surrounding areas worst hit by Covid-19 will not reopen until January 18, with students elsewhere in England expected to return to class this week.
Health Secretary Matt Hancock insisted it was safe for primary schools to reopen in all but the worst hit areas and teachers were at no greater risk of contracting Covid-19 than the rest of the population.
But a statement – signed by the NAHT school leaders' union, the National Education Union (NEU), the NASUWT teachers' union, GMB, Unison and Unite – calls for a move to remote learning for most pupils.
All staff continuing to work in schools with vulnerable pupils and children of key workers should be given priority access to Covid-19 vaccinations, it adds.
The statement says: "Bringing all pupils back into classrooms while the rate of infection is so high is exposing education sector workers to serious risk of ill-health and could fuel the pandemic."
The education unions are calling on the Prime Minister to order a "pause" in a return to the classroom until the safety of staff and pupils can be guaranteed.
They say Boris Johnson should sit down with unions to "discuss a joint approach" to ensure there are safe working arrangements in schools, and pupils have the equipment they need to receive remote learning.
TUC general secretary Frances O'Grady said: "The Government's own advice from Sage makes it clear that opening schools to all pupils now risks increasing the infection rate. That's in no-one's interests.
"Instead of creating chaos for parents and exposing workers to risks, the Prime Minister should be talking to trade unions about what steps are needed to make sure all schools are Covid-secure."
NASUWT general secretary Dr Patrick Roach added: "It is now abundantly clear that the pandemic is seriously impacting on the ability of all schools and colleges to continue to operate normally.
"The NASUWT is calling for an immediate nationwide move to remote education for all pupils in primary, secondary and special schools and colleges."
It comes after the NEU advised its members that it is not safe to return to classrooms on Monday.
Gildersome Primary School in Leeds, which is in Tier 3, has been forced to shut to most children indefinitely after 16 staff signed a letter saying they are "exercising their right not to teach full classes".
But Mr Hancock told Sky News that it is "clear that the proportion of teachers who catch coronavirus is no higher than the rest of the population".
He added: "So there is clear public health advice behind the position that we have taken and that is what people should follow because, of course, education is very important as well, especially for people's long-term health."
Secondary schools and colleges in England will have a staggered return, with those taking exams this year resuming in-person teaching on January 11 and other year groups on January 18.
Testing kits are being sent out to secondary schools and colleges this week in preparation for the mass testing of pupils when they return to class.
But confusion remains among teachers and parents about school closures following last-minute Government announcements over the Christmas holidays about the delayed reopening of some schools.
And a number of councils – including Cumbria and Kent – have urged the Government to allow all primary schools in their areas to remain closed.
NOTICE TO MEMBERS AND PARENTS: This morning we have to #MakeSchoolsSafe to #ProtectCommunities. Below is the guidance to our members to make themselves available for online learning.https://t.co/bhyHtXsR0O
— National Education Union (@NEUnion) January 4, 2021
Bryony Baynes, head of Kempsey Primary School in Worcestershire, said she feels "frustrated" at the lack of clear leadership over the issue.
She told the PA news agency: "I feel sick with anxiety. I emailed all my staff last night because I am aware that the NEU has issued guidance letters and all of my staff are committed to being in school.
"They are, as I am, very anxious, but are determined to do their best for the children in our care."
Ms Baynes added: "I have to depend on the DfE [Department for Education] and my local authority to lead me and, at the moment, I don't feel that leadership is clear."
One parent, who asked to remain anonymous, said she would not be sending her children to school due to her coronavirus safety concerns.
As she has severe asthma, the woman told PA she could not risk her children bringing the virus home so she would be teaching them herself.
She said: "We have all managed to avoid catching Covid so far, but with this new strain, I don't think it's safe at all."