Teaching unions have demanded that the government to "step back" from plans to re-open schools on June 1 over fears it cannot be done safely.
It comes as Education Secretary Gavin Williamson accused teachers of "scaremongering" over their fears that the return to school is being rushed.
Prime Minister Boris Johnson said on Sunday that he hoped primary schools would re-open to pupils from Reception, Year 1 and Year 6, on June 1 "at the earliest", if infection rates and the government's other tests at the time allow it.
The statement is signed by nine unions and calls on ministers to work with them to create safety standards that they believe could work.