Schools in Germany are advising pupils to bring blankets to class and wear hats, coats and scarves during lessons as part of the fight against the coronavirus.
Head teachers have issued the advice in response to new government guidelines that require schools to ventilate classrooms by opening the windows every twenty minutes.
Leaving the windows open a crack is not enough. Schools have been told to open classroom windows fully for three to five minutes, and to open doors as well when possible so air can circulate.
With winter temperatures often well below zero, no one is under any illusions about how cold classrooms could get.
A sixth form college in Bochum has advised pupils to bring "warm clothes with hoods or hats and blankets" to class, and secondary schools in Düsseldorf are allowing pupils to wear coats and gloves during lessons.
In a letter to pupils, the regional education minister for Lower Saxony warned that "things will get a little cold" and urged them to "dress warmly".
Doctors have spoken out against the new government regulations, warning they will cause a wave of colds and other infections.
"The rules are absurd,” Dr Stephan Pilsinger, a Munich GP turned politician told Bild newspaper. "They're a health hazard."
"During the cold months, thick sweaters, scarves and blankets will now be part of the basic equipment for schoolchildren", said Susanne Lin-Klitzing of the Philologenverband teachers' union.
She said staff and pupils would have to dress "according to the onion principle" — with multiple layers they can remove as classrooms warm up between ventilation times.
But she accused regional governments of failing to plan adequately for the cold months and said if they'd had more warning schools could have put up plastic shields between pupils to avoid infection.
Germany was one of the first European countries to reopen schools following the first wave of the pandemic, and returned to full class sizes at the end of the summer holidays.
But ever changing government advice has resulted in a series of embarrassing U-turns. The regional government in Hamburg bought 30,000 transparent plastic head visors to distribute to schools in August.
But it has now told schools they do not provide sufficient protection and should not be used. Pupils and staff are required to wear facemasks while moving about instead.