More schools are advising pupils and staff to wear face coverings to help combat coronavirus.
Grantown Grammar School in Grantown on Spey and Millburn Academy in Inverness have both said masks need to be worn between classes.
Children across Scotland are not currently required to wear masks in either primary or high schools.
But Nicola Sturgeon has said this advice could change for secondary school students in the “near future”.
The World Health Organisation (WHO) has issued fresh guidance saying children over the age of 12 should wear masks and the EIS trade union posted a message on Twitter that it will “will press [the] Scottish Government further on face covering protocols in light of WHO advice”.
In a letter to parents, Grantown Grammar School explained the changes are being introduced because “corridors are becoming crowded between lessons and at break and lunchtime, even with the one way system”.
Similar concerns about overcrowding as pupils move between lessons sparked the introduction of face coverings at James Gillespie’s High School in Edinburgh.
The letter to parents at Millburn Academy in Inverness also asks for face coverings to be worn on school buses.
The Scottish government has said there is currently no evidence that coronavirus among young people is being transmitted in schools.
A growing number of school pupils have tested positive for Covid-19, but the government believes the infection has been transmitted in other settings, such as house parties or other indoor gatherings.