From next week primary schools with capacity to accommodate maximum class sizes of 15 pupils will be encouraged to welcome back all year groups.
The new guidance comes after the government was forced to shelve its plan for all primary school children to have at least a month of classroom education before the summer holidays.
The Labour Party has said the short notice of the announcement will contribute to “widespread confusion” for schools, pupils and parents.
Currently only reception, year one and year six have been allowed to return, and many reopened schools have not been able to accommodate all three groups.
Last week in the House of Commons, Education Secretary Gavin Williamson said: “While we are not able to welcome all primary children back for a full month before the summer, we continue to work with the sector on the next steps, where we would like schools that have the capacity to bring back more children – in those smaller class sizes – to do so if they are able to before the summer holidays.”
Labour’s shadow education secretary Rebecca Long Bailey said the announcement of new guidelines without clear advance warning could create further uncertainty for schools, pupils and parents.
“There’s widespread confusion across the sector, and the government so far has failed to build a consensus between school leaders, trade unions, leading experts within the sector around the safety principles that need to be put in place within schools for a safer wider reopening,” she told Sky News.
“There’s a feeling that schools and local authorities have been left to navigate this by themselves, and that should never have been the case.
“What the government should have done from the start is create a task force to reach a consensus, not only to ensure safety principles were put in place, but also to provide reassurance that it was safe to go back into the classroom, and that didn’t happen. The government has to work very quickly to rebuild trust.”
Labour has also called on ministers to reconsider the decision to withdraw funding for free school meals and meal vouchers over the summer holidays.
Last week, the prime minister promised a “massive catch-up operation” to help school children who have missed out on education.
Although schools will not be expected to open over the summer, the government’s hope is that a support package will be in place through the holidays and into the next academic year.
Ministers insist they are working with local authorities to ensure all schools can reopen in September, if it is deemed safe to do so.
A Number 10 source said Mr Johnson had “ordered detailed plans to be rapidly drawn up”.
“The PM is acutely aware that school closures will have a disproportionate impact on all children, and particularly the most disadvantaged and vulnerable children.
“He appreciates the consequences of months out of school, and this package will be focused on providing extended support for children.
“The PM is so grateful for the hard work of teachers, parents and schools to keep educating children throughout this difficult period.”
But in an interview with The Observer, the children’s commissioner for England said the government had not moved fast enough, and risked violating the basic right to education enshrined in a UN convention.
“It has taken 200 years of campaigning to get children out of the workplace and into the classroom, ensuring that education was a basic right for all children,” Anne Longfield told the newspaper.
“We seem for the first time to be prepared to let that start to go into reverse. And I think that is a very, very dangerous place to be.
“We heard from the prime minister back in April that education was one of the top three priorities for easing lockdown, but it seems to have been given up on quite easily.”
The Department for Education claims progress is being made on getting children back to school, pointing to survey results which show 70% of 18,000 primary schools who responded have opened for eligible year groups.