My HS in central NJ had neither windows in the classrooms, nor WALLS. It was designed like a giant open office bullpen thing and classes were supposed to congregate in vaguely defined areas. By the time I got there in the early 90s, they had already erected borders everywhere out of movable chalkboards, so you basically got a traditional classroom layout but with noise pollution from all the other classes going on nearby. Great job all around. (Though I suppose from the CO2 standpoint we were probably doing better than most!)