[Wonder Warthog]

"But don’t classroom doors open outward?"

Bars work both ways. If the door opens inwards, the "receivers" (not sure exactly what these are called....those "Z" shaped pieces of metal that the bar slots into) are on the doorframe. If the door opens outwards, the "receivers" are on the door.

[Hoffer Rand]

I didn’t read far enough down thread. I see your answer. That would work.