Pupils in Scotland and Northern Ireland now have to wear face masks in school corridors and communal areas to reduce the risk of coronavirus transmission.
The new rules, which kick in today, apply to all children over 12 in Scotland – and on school transport for primary pupils five and above.
In Northern Ireland, post-primary pupils and teachers will also have to wear face coverings in corridors and communal areas. Masks on school buses are strongly recommended but not mandatory.
Face coverings are not mandatory in classrooms in either country.
Scottish schools reopened on 11 August and the harder line on masks comes after 17 members of staff and two pupils recently tested positive for COVID-19 at a school in Dundee.
In England, the government made a U-turn last week when it decided that masks should be mandatory in secondary schools – but only in regions where lockdown measures are in place due to an increase in local cases.
The change came after pressure from headteachers, teaching unions and medical experts.
“What we’re saying is if you’re in a school where there is a ‘hot spot’ then it probably does make sense in confined areas outside the classroom to use a face coverings in the corridor and elsewhere,” said Prime Minister Boris Johnson.
England’s deputy chief medical officer, Jenny Harries, said recently that evidence on whether children over 12 should wear masks in schools was “not strong”.
But Mr Johnson said the government had changed tack to follow the latest World Health Organisation advice.
The Welsh government has only recommended face coverings in communal areas of secondary schools where social distancing is not possible.
The advice also applies to pupils over 11 on school transport, along with college students and staff.
It will require schools and local authorities to carry out risk assessments of their sites to determine if the two-metre rule cannot be maintained.
The new rules come as a survey found nine in 10 teachers believe they won’t be able to socially distance from both pupils and other staff.
The Tes poll of 6,000 school staff in England – which took place at the end of last term – found 86% believed minimising contact between pupils would not be possible, while two thirds (66%) thought guidance to avoid busy corridors, entrances and exits was unrealistic.
A third felt the government approach to coronavirus safety in schools left them “at risk”.