It is “vitally important” children go back to school, with the life chances of a generation at stake, Boris Johnson has said in a message to parents.
As the autumn term begins in Northern Ireland, the prime minister said the risk of contracting coronavirus at schools across the UK was “very small”.
He said missing any more school was “far more damaging” for children.
Meanwhile No 10 said it has “no plans” to follow Scotland in reviewing rules on wearing face coverings at school.
First Minister Nicola Sturgeon said the move was in response to the World Health Organization (WHO) issuing guidance saying children over the age of 12 should wear masks.
But a Downing Street spokesman said no such review was planned for England’s schools, adding: “We are conscious of the fact that [face masks] would obstruct communication between teachers and pupils.”
Classroom buzz, sanitiser stations and more masks
How many confirmed cases are there in your area?
In Scotland, schools have already reopened. Some pupils in Northern Ireland returned to school on Monday, while term starts in England and Wales in September.
Mr Johnson thanked school staff for spending the summer “making classrooms Covid-secure”, in a statement released on Sunday evening.
Citing comments from England’s chief medical officer Prof Chris Whitty at the weekend, Mr Johnson said the risk of catching coronavirus in school was “very small and it is far more damaging for a child’s development and their health and wellbeing to be away from school any longer”.
“This is why it’s vitally important that we get our children back into the classroom to learn and to be with their friends,” he added.
“Nothing will have a greater effect on the life chances of our children than returning to school.”
And in a video message shared on Twitter, he said the “best way” to help children with any mental health problems resulting from or exacerbated by lockdown was “to get our kids into school”.
Prof Whitty said on Sunday that children were more likely to be harmed by not returning to school next month than if they caught coronavirus.
He cited evidence of children “much less commonly” needing hospital treatment or becoming severely ill with coronavirus than adults.