Face coverings will no longer be compulsory in England's secondary school classrooms from 20 January.
The announcement was made by the prime minister, as part of the easing of "Plan B" Covid measures.
What's happening this term?
All UK schools are expected to offer face-to-face teaching to every age group, and to provide effective online learning for pupils who are absent or isolating.
The specific Covid measures in place vary across the nations.
All school staff and secondary school pupils are asked to take two lateral flow tests (LFTs) a week (three in Wales).
In England, the latest advice ends the requirement for secondary school pupils to wear masks in class as well as in communal areas.
In Wales, some schools have reintroduced year group bubbles, and have staggered start and finish times.
In Northern Ireland, schools are reopening with the same measures in place as last term.
In Scotland, social distancing remains in place, pupils are separated into groups where possible, and teachers are required to wear masks when in close contact with pupils.
What are the risks of schools staying open?
There are two main risk factors:
- pupils bringing Covid into school following family gatherings over Christmas
- infections among teachers and other school staff leading to class or even school closures
The latest data shows 8.6% of teachers were absent during the first week of term in England, with 4.9% off because of Covid, up from 3% on 16 December. In addition, 8.9% of teaching assistants and other staff were also absent.
The problem was slightly worse in primary schools than in secondaries, where pupils must wear face masks in class.
Many schools have told the BBC they can't find temporary staff to cover the teachers who are off. A number of supply teachers are already working in tutoring organisations as part of education recovery plans.
Meanwhile, 315,000 (3.9%) pupils were absent for Covid-related reasons in the first week of term, up 14,000 before the Christmas holiday.
England's Education Secretary Nadhim Zahawi says the government is considering options to deal with staff shortages.
He previously urged retired teachers to return and join teacher supply agencies to fill gaps, but a BBC survey suggests there has been a limited response.
Mr Zahawi also suggested schools could merge classes in the event of teacher shortages.
But teaching unions said there were logistical difficulties and safety issues with teaching large groups of children.
What happens if there is an outbreak?
Under England's guidelines, a school must get in touch with public health officials if five pupils, teachers or staff in close contact test positive for Covid in a 10-day period.
School management must then work with local health officials to mitigate the spread of disease.
- encouraging home testing or increasing its frequency
- on-site rapid testing in secondary schools, colleges and universities for two weeks
- extra cleaning and more ventilation
Can a child go to school if someone in their household has Covid?
Yes - as long as they don't have any of the main Covid symptoms, under-18s don't have to self-isolate if someone else in their household has Covid. Similarly, whole classes are no longer automatically sent home if a pupil or teacher tests positive.
However, if they are over five years old, close contacts are strong advised to take LFTs for at least seven days.
Which pupils are being vaccinated?
All children aged 12 and over are being offered two doses of the Pfizer vaccine, with the second jab typically given 12 weeks after the first.
The Joint Committee on Vaccination and Immunisation (JCVI) has also recommended that booster doses should be offered to children aged:
- 16 and 17
- 12 to 15 if they are in an at-risk group or live with someone who is immunosuppressed
- 12 to 15 who have a severely weakened immune system, who should get four doses
A low-dose version of the Pfizer vaccine has also been approved for five to 11-year-olds who have health conditions that put them at greater risk from catching Covid.
The JCVI also recommended that primary school children who live with clinically vulnerable adults should also be offered a jab, but it's not yet clear when children might get the doses.
Children who aren't considered to be at high risk from Covid should wait 12 weeks after testing positive for Covid before being vaccinated.
What about ventilation?
Ventilation is one of the key measures designed to keep schools safe from Covid.
In England, the government is making 7,000 air cleaning units available to early years settings, schools and colleges.
Labour says this isn't enough, but the Department for Education says the units are only required in areas where doors and windows cannot be opened effectively.
Some 300,000 carbon dioxide (CO2) monitors had already been promised for England's schools to help identify areas with poor ventilation, but teaching unions complained this won't solve the problem.
The Scottish government gave £100m to local councils to help fund Covid improvements, including hygiene measures and ventilation.
The Welsh government has a £6m programme to increase air circulation and purity which will provide 30,000 CO2 sensors and 1,800 ozone disinfecting machines.