This was obviously from a long time ago, but:
One of the elementary schools I attended had classrooms around the outside, most with windows...and windows that could be opened at that! (well, untill they went around & screwed them all shut due to kids unlocking/nobody noticing/sneaking in at night). Some had exterior doors as well
Then 4 main hallways around, with exterior doors at the ends of some
And a central bank of classrooms in the middle.
The "walls" between classrooms (and some hallways) were simply panels that clamped to the grid ceiling & were (I believe) screwed/bolted to the floor, and no doors on any of the rooms. Obviously done so rooms could be fairly easily re-configured.
But even where there were normal walls (one main hallway, restrooms, offices, etc), they only went up to the ceiling...the space above the ceiling was open over the entire school (except the gym since that was taller)
With that sorta setup (wall panels clamped to the ceiling grid), if you woulda lost the roof (and along with it the grid) most of the classroom walls would simply have fallen over...The safest place probably would have been in one of the offices.
They didn't do tornado drills or anything other than fire drills.
That said:
* We don't get tornadoes here. (I know "never say never" but the chances of anything are so rare...)
* The school was completely gutted & re-done (plus added on to) after I left. With actual walls/doors on classrooms/etc (codes had been upgraded since the time it was built...plus the old design was pretty noisy being so open.)
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I have a feeling that there probably were allot of older school buildings with simple (and maybe not so safe) construction like that around....maybe even still some too.