That can be easily automated, and has been in a variety of ways. Just plug a USB or an Ethernet port, press 1-2 keys and done. The sysadmins won't have to go through a normal install wizard.
But with a LAN port, wouldn't you agree that reinstallation could take 1-2 human minutes of work, even if the whole process takes an hour? Take the laptop, plug it in, press a key, wait however much, then take it out and give it back to the student. The student could even do it themselves.
And even without a LAN port I assume there are various ways to automate it so it isn't really an issue. If you keep /home or if most files are synced, students could break their OSes every day if they want to. One of those students will actually learn from it, at least.
