The Welsh government has recommended the use of face coverings in communal areas of secondary schools where social distancing is not possible.
The new guidance 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.
A joint statement by health minister Vaughan Gething and education minister Kirsty Williams said: “The current advice from the Chief Medical Officer for Wales is that face coverings are recommended for all members of the public over 11 years in indoor settings in which social distancing cannot be maintained, including schools and school transport.
“We will amend our operational guidance for schools and FE to require settings and local authorities to undertake risk assessments of their estates to determine if face coverings should be recommended for their staff and young people in communal areas. This will also include school and college transport.”
Mr Gething had asked a scientific advisory group to consider the current coronavirus guidance for the nation’s schools, which are due to return next week.
Scotland and Northern Ireland are mandating the use of face coverings in secondary school corridors and communal areas.
They will be required in secondary school corridors in parts of England under local lockdown, after a U-turn by the government.
Teaching union NAHT Cymru said it was “unacceptable that school leaders are expected to shoulder the responsibility of deciding if face coverings are required in schools”.
“Headteachers are not medical experts and the Welsh Government should not put them in this position,” the union’s director Laura Doel said.
But David Evans, Wales Secretary of the National Education Union Cymru, welcomed the statement.
“To us the statement is clear – in areas where social distancing can’t be maintained, face masks need to be worn by everyone over 11 years, including in schools and on school transport,” he added.