I can't speak to the classroom speaker configuration, at least off the top of my head. But sending different mixer inputs to each shop speaker is just a matter of turning the balance knobs on the mixer to send your desired source to either the left or the right channel.

when it was set up, the speaker system could play back mp3, streaming computer, and microphone to classroom and/or shop, and send say computer to classroom and mp3 player to shop.

i've no clue if someone has yet again "fixed" it so that doesn't work, but i can look at it and get it reset to that again this evening.

Yes, the system works like that again, when I was there last week. The front aux input jack on the stereo can be used for input. By default it's connected to the PC, but anyone can plug another device into that jack instead. My concern about the present configuration was whether or not the two shop speakers were configured always as left/right. Since they're each now in different areas, I'd think it better if both would most always produce combined l/r mono sound, except when stereo is needed for single-room use. One thing that's wonky is the radio antenna connection on the back of the stereo, which is bare wire and not a proper plug.

iirc they were set up as mono, but each could be controlled as relative volume, although that was a bit more awkward.

not ideal as summing a stereo signal doesn't always do what you'd expect (depending on how it was engineered) but it's usually fine.