I am surprised about your comment. What do you find hard to believe? I am from (western) Germany, and I find it hard to believe, that there are class rooms without windows. Except for one or two special purpose rooms, in my school time, I have never ever seen a class room, which didn't have windows on one long side. The other long side would be towards the hallway. The rooms almost never needed artificial lighting (unless in the first hour in the Winter or really bad weather) and plenty of fresh air when opening the window. Daylight and fresh air are the best ways to keep the pupils awake.