Scottish secondary school pupils will have to wear face coverings in corridors, communal areas and school buses from next Monday.
Education Secretary John Swinney said the new rules would apply to all pupils aged over 12.
There will be no requirement to wear face coverings in classrooms where distancing measures are in place.
Mr Swinney said individual exemptions could be granted for health reasons, but the guidance would be “obligatory” for all secondary, special and grant-aided schools.
He told the BBC’s Good Morning Scotland programme: “From August 31st young people over the age of 12 in secondary schools should habitually be wearing face coverings when they are moving around schools and corridors and in communal areas where it is difficult to deliver the physical distancing.”
He said the Scottish government had acted in the light of the new WHO advice based on evidence that teenagers can infect others in the same way as adults, but had decided to go further by extending it to school transport.
“It’s part of the general measures we are taking to ensure we keep pace with the emerging advice about how to keep our schools open and to keep our schools safe,” he said.