[eru]

German schools open their windows in winter.

It's the classic German Stoßlüften in action.

However, the air outside also has lots of dusts. Opening the windows does nothing for that, but air filtration can potentially help.

[dzhiurgis]

We did it too, but it was huge ceremony around it. Kids shouldn’t be begging and screaming “too cold” for fresh air.

[eru]

The ceremony is part of the fun.

Though for us the ceremony was only one or two mild complaints from the kids near the window, and the teacher firmly stating that the room reeks of sweaty teenagers and needs some airing out.