I basically did that by using Oracle's always free VPS [1] and we set up a jitsi instance. We did our Scholastic Bowl practices over it. But Oracle just killed my VM and said "System terminated your account and unfortunately we can't reactivate or restore the account. Thank youfor chatting with us. Have a good day". Should have seen it coming from Oracle...
With regular back-up so that when a student inevitably mess up beyond repair (rogue rm or dd command or something modifying his path) he can time-machine like roll back to a previous version.
Then you get to enjoy the show. Someone will inevitably start pen-testing the school. Why is one machine constantly maxed-out? Is that a Quake server they are running? Oh they have their own chat client/protocol now, interesting. Basically https://en.wikipedia.org/wiki/Incompatible_Timesharing_Syste...