Parents have been told children at Barr Beacon School in Aldridge will not be allowed to wear coats during winter, even though windows will be kept open due to coronavirus meaning classrooms will be colder.
They will, however, be able to wear vests or T-shirts under their uniform, the school has said.
Barr Beacon School, on Old Hall Lane, has around 1,500 pupils.
Headteacher Lynsey Draycott was quoting a report from the Government's Scientific Advisory Group for Emergencies (SAGE) in a letter to parents, saying they had warned children would have to "get used to being cold".
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She said "uniform policy" meant coats would not be allowed to be worn in the classroom. But the school said it hoped the extra layer under pupils' uniforms would stop them being cold.
The letter, dated September 11, said: "The Scientific Advisory Group for Emergencies (SAGE) has warned that, because school windows must be left open to fight coronavirus, pupils should start wearing more clothes and “get used to being cold”.
"Pupils will not be allowed to wear coats in classrooms but they may choose to wear plain, white vests and T-shirts below their shirts and/or a black V-neck jumper, in accordance with our existing uniform policy."
The school said in a statement: "Barr Beacon School’s first priority is the safety and wellbeing of its pupils and staff. To ensure we keep our children safe the school has shared with parents the steps taken to minimise the risk of viral transmission.
"Government advice has been to encourage the through flow of air to reduce transmission. To prevent children from being cold the school suggested that pupils could wear an extra vest or T-shirt under their school uniform. Many parents have thanked the school for the information and advice that has been sent home and the support their children have received.
"All we are trying to do at Barr Beacon is keep our children and staff as safe as possible.”