Pupils in year 7 and above, plus staff and visitors, are being “strongly advised” to wear a face covering under the “temporary and precautionary” measure, which will take effect from Monday.
Masks will not be required in classrooms and exemptions will remain in place for those who have a medical reason not to wear one.
Nadhim Zahawi, the education secretary, said the measure was a “targeted and proportionate action as a precaution while we find out more information about the new variant”.
He added: “We will continue to prioritise children’s and young people’s education and wellbeing, making sure education and childcare settings are as safe as possible and children continue to benefit from classroom teaching.
“We are working with education and childcare settings to enhance safety measures where needed, including introducing isolation for 10 days for close contacts of suspected omicron cases.”
Students in Year 7 or above should also continue to wear face coverings on public and dedicated school transport, unless they are exempt, the Department for Education (DfE) said, and staff and students should continue to be encouraged to test themselves twice a week using lateral flow tests.
The department also said schools, out of school settings and colleges will “want to consider” whether to go ahead with any planned international trips at the current time, given the potential risk to education from the need to isolate and test when returning to the UK.
The Association of School and College Leaders (ASCL) backed the move, saying it was a “sensible response to the risks posed by the omicron variant of Covid-19”.
Geoff Barton, ASCL’s general secretary, said: “It appears that the omicron variant may result in more staff and pupil absence thereby worsening an already very grave situation.
“It is therefore imperative that the government provides workforce funding to schools and colleges to help with the cost of supply cover for absent staff.
“Schools and colleges are in a position of having to provide in-class teaching for some groups of students, and remote education for other groups of students, at the same time as experiencing Covid-related staff absence. They simply cannot sustain the ongoing costs of the supply cover that is required.”
Kevin Courtney, joint general secretary of the National Education Union, said: “We welcome the DfE guidance that masks must be worn by adults and children in Year 7 and above in communal areas.
“We think the DfE should go further and encourage mask-wearing in secondary classrooms and also plan investment to improve ventilation and air filtration.
“These steps can all help reduce the spread of Covid and thereby reduce disruption to education. Omicron makes the threat of disruption of education all the clearer: any close contacts of an omicron case, staff or pupils, will have to self-isolate for 10 days, whether vaccinated or not.”