Secondary pupils in Scotland are to be ordered to wear face masks in school corridors and other communal areas but not classrooms, under plans outlined by Nicola Sturgeon.
The First Minister said different groups of pupils are more likely to mix and transmit the virus in these areas thanks to crowding and a lack of ventilation.
Speaking at her daily briefing, she said her government was in the final stages of consulting on the change and an announcement will be made within the next few days.
Although SNP ministers are not consulting on introducing masks into the classroom, she said they could be an option where there are outbreaks. Ministers are also considering whether masks must be worn on school buses.
Ms Sturgeon highlighted new guidance issued by the World Health Organization (WHO) over the weekend that "children aged 12 and over should wear a mask under the same conditions as adults", particularly where they cannot maintain a metre social distancing from others.
She said schools would be responsible for introducing the change in the first instance but it was unclear how it could be enforced if a pupil refused to wear a mask.
Young people returned to Scotland's schools earlier in August with no requirements for physical distancing between younger pupils, and no rules around face coverings.
Some Scottish schools have since requested that pupils voluntarily wear coverings in some circumstances, including schools in the Highlands and James Gillespie's High School in Edinburgh.
But parents campaign group Us For Them Scotland, which has 9,500 members, opposed the move by arguing it would "cause more harm than good".
The group cited an intervention by Prof Chris Whitty, England's chief medical officer, that the chances of children dying from the virus are "incredibly small" and they much less commonly become seriously ill.
Ms Sturgeon said: "We're consulting on this specific measure because, firstly, mixing between different groups is more likely in corridors and communal areas - increasing the potential for transmission.
"Secondly, crowding and close contact in these areas is more likely and voices could be raised, resulting in greater potential for creating aerosol transmission. Finally, there's also less scope for ventilation in these areas."
However, she said they were "not currently consulting on any proposal" to have pupils wear masks in class, saying: "There is greater scope for physical distancing in classrooms and [face coverings] are more likely to interfere with teaching and learning."
She said there would be exemptions for pupils with medical conditions such as asthma and ministers were examining providing masks for pupils who had failed to bring one to school.
Ms Sturgeon added: "We are not talking about a mandatory system in the sense of there being penalties and enforcement in schools. I get the sense that schools - while I accept there will be a mixture of opinion around it - are themselves looking to follow this kind of approach."
A recent survey of nearly 30,000 teachers by the Educational Institute of Scotland teaching union found 41 per cent supported the mandatory wearing of face coverings by senior pupils in classrooms.
Larry Flanagan, its general secretary, said the union still believed physical distancing was the best way to stop the virus spreading in schools but welcomed the consultation on using face masks "where physical distancing is difficult."
But Jo Bisset, organiser for Us for Them Scotland, said: "Forcing children to wear masks when there’s little, if any, scientific evidence to support such a move could be hugely damaging.
“It could have an extremely negative impact on pupils with autism, hearing impairments and conditions such as asthma."
She added: "Parents want to get their children back to school and for that experience to be as normal as it possibly can be."
Willie Rennie, the Scottish Liberal Democrat leader, said: "This change of policy is the right thing to do and will provide an extra barrier of protection from the virus and reassurance to staff, pupils and parents."