Some UK schoolchildren will be able to return to the classroom as part of a phased return as early as next month, the government said.
But teachers' unions are questioning the timetable and want urgent talks with the government and guarantees of safety.
UK Education Secretary Gavin Williamson said primary school children in reception, Year 1 and 6 and secondary school pupils in Years 10 and 12 would return first, but in smaller classes.
Mr Williamson said children would be kept within those smaller groups, while schools will adhere to “rigorous” standards of hygiene and cleaning.
On Saturday, Mr Williamson said another 244 people had died in the UK from Covid-19 in the previous 24 hours, taking the country’s death toll to 34,242.
Government talks with unions had stalled over the return plans.
Mr Williamson said the government would continue to consider all advice before the June 1 schools reopening.
Jenny Harries, England's deputy chief medical officer, said that teachers "should not be thinking that every school is likely to be swarming with cases", and that the risk was low.
The UK has had the worst coronavirus death toll in Europe and six weeks of severe lockdown conditions.
"It is urgently important that the Government takes every available opportunity to provide the necessary assurances that teachers are seeking," said Dr Patrick Roach, general secretary of the NASUWT teachers' union.
“It should not be forgotten that teachers have continued to look after vulnerable children and children of critical workers while also providing high-quality support for remote learning for children who are at home.
“Schools are looking to the government for clear and unequivocal guidance on the health and safety measures they will need to have in place prior to reopening.
“The bottom line is that no teacher or child should be expected to go into schools until it can be demonstrated that it is safe for them to do so.”
Meanwhile, the National Education Union said it also wanted talks with the government about when it would be safe to reopen schools.
“We will take up Mr Williamson’s statement that his door is open in order to seek to engage in discussions about a safe way forward,” said Kevin Courtney, joint general secretary of the NEU.
