Thousands of pupils will begin to return to school in England after months of remote learning.
All children will be able to return to class from Monday under the first step to ease restrictions, but secondary schools can stagger the return of students over the week to allow for mass testing.
Secondary school pupils are being asked to take three voluntary Covid-19 tests on site and one at home over the first fortnight. They will then be sent home-testing kits to do twice-weekly.
The Department for Education (DfE) is also advising secondary school students to wear face coverings wherever social distancing cannot be maintained, including in the classroom.
But primary school children are not being asked to carry out Covid-19 tests or wear face masks on their return.
It comes as Prime Minister Boris Johnson said there were dangers involved in keeping classrooms shut for too long when asked about the risks of schools returning.
He said on Sunday: “I think the risk is actually in not going back to school tomorrow given all the suffering, all the loss of learning we have seen.
“I do think we are ready, I think people want to go back, they feel it, they feel the need for it.”
Separately on Sunday, Amanda Spielman, England’s chief schools inspector, expressed concern about eating disorders and self-harming among some children after she said pupils had endured “boredom, loneliness, misery and anxiety” during two months stuck at home.
Pupils in England, except children of key workers and vulnerable pupils, have been learning remotely since the start of the lockdown in January.
The latest Government figures show that more than one in four (27%) primary school pupils in England were being taught on-site in the week after half-term.
Overall, nearly a fifth (18%) of state school pupils were in class on February 25, up from 16% on the week before half-term, according to the DfE statistics.
An Institute of Fiscal Studies (IFS) survey suggests that nine in 10 parents would send their child back to school this week even if it was optional.
The Government has introduced asymptomatic coronavirus tests for secondary school and college pupils – as well as tougher measures around face masks – ahead of the full reopening.
But school leaders have been struggling to get parents’ permission for the voluntary tests, and some are concerned that pupils will refuse to wear face coverings in classrooms as they are not mandatory.
A survey by the Association of School and College Leaders (ASCL) found that more than half (52%) of heads have faced difficulties in securing parental consent for pupils to take part in regular rapid Covid-19 tests.
Paul Whiteman, general secretary of school leaders’ union NAHT, said: “This is a special week. It will be good to hear the sounds of more young people back in classrooms and school playgrounds again after the latest lockdown.”
But he added: “Whilst there is a great deal of excitement about children returning, there is understandable anxiety too.
“It is therefore essential that the Government monitors the early data following the wider reopening very closely and acts accordingly.
“Equally, the Government must do more to ensure that the return to school is a sustainable one. Further improving safety measures in schools would help reduce the chance of future disruption.”
In Northern Ireland, the youngest children will also return to primary schools on Monday, but they are set to go back to remote learning after two weeks.
In Scotland, children between the ages of four and eight in primaries one to three returned to school last month, alongside some secondary pupils who needed to do practical work.
All primary school pupils in Scotland are due back in classrooms on March 15, while secondary pupils are likely to receive some in-school education each week before the Easter break.
Children aged between three and seven also started a phased return to school in Wales on February 22, and some vocational learners were back at college for their practical qualifications.
All primary school pupils in Wales, as well as older age groups in Years 11 and 13 who have exams, are expected to return from next week.