Pubs will have to close to keep schools open if there is a local outbreak of Covid-19 next month, No 10 has confirmed.
Schools will be the “absolute last” group to close in a local lockdown, Downing Street said.
Other venues, such as pubs and restaurants, will be expected to shut their doors first.
Boris Johnson has insisted that schools are safe for pupils to return in September.
The prime minister has also said the country has a moral duty to get children back in the classroom.
But he is facing pressure from teaching unions and the children’s commissioner for England, who has called for more routine testing of pupils and staff.
Ministers have rejected the calls, saying the current safety standards are sufficient.
No 10 said it was a national priority to get and keep schools open and that Mr Johnson had confidence in the Education Secretary Gavin Williamson.
The prime minister’s official spokesman said: “It is correct to say schools would be the absolute last sector to close in any local lockdown.
And other venues would be expected to be closed first in the event that strict lockdown measures had to be applied.”
However, under the current local lockdown there is nothing in the rules to prevent schools re-opening in Greater Manchester and other areas.
Many pupils who return to school will do so for the first time in months.
In a bid to allay fears, Ms Williamson said there was “little evidence” to suggest coronavirus is transmitted at school.
He added: “We have always been and will be guided by the best scientific and medical advice.
“The latest research by Public Health England which is expected to be published later this year – one of the largest studies on the coronavirus in schools in the world – makes it clear there is little evidence that the virus is transmitted at school
“There is also growing confidence among parents about their children returning. This is down to the hard work of school staff across the country who are putting in place a range of protective measures to prepare to welcome back all pupils at the start of term.”
His comments were echoed by a leading child health expert professor Russell Viner, who said a Public Health England (PHE) study, which has not yet been published, will conclude that “children play a minor role in the transmission of the virus and schools play a minor role in the transmission of the virus”.