It's only shown once to the student. As soon as they choose to accept or decline, their preference is saved. So long as that preference file is there, they won't see it again. You can remove the preference file with a quick windows search for "aup.ini" and it'll pop right back up again.
It determines staff / students with a username prefix. Our school uses "stf" to prefix its staff users but you can change this in the config file. If I find a better way of doing this, I'll update the code but it's a case of making it work for the majority of schools.
I hope that answers a few questions. Drop me a PM if you need advice on setting it up.