This is what China currently gives the American consumer ... reasonably high quality goods at very low prices. However, they don't export school buildings ... yet. So we must do it for ourselves.
Here is my solution
This is a concrete dome, the kind they make for storage purposes ... like a big dome over a salt stash. You keep your salt dry till you need to put it on the road in winter. Or, some big warehouse type thingy.
As you can see, it could get really elaborate and there is no reason to do the square "box" thing.
In the plan, the partitions are possibly temporary, changeable structures so that more rooms could be squeezed into the same space or larger ones made. The thing on top of the dome is a whole school fan ... open in summer to assist AC cooling and closed to the outside in winter and used as an overhead fan (possibly ducted to halls or rooms via the ceiling).
A cement dome, sprayed onto a "balloon" form will not leak, is very strong and requires little maintenance ... and ... it's cheap. If it's ugly ... well, beauty is in the eye of the beholder. And I'll bet a good architect could make it look very stylish anyway.
And it's cheap and simple.
Another major factor in this type of building is it's low cost and high quality.
But the greatest factor to consider is that it is relatively inexpensive.
And did I mention that you, as a taxpayer, wouldn't have pay much in the way of new taxes?