While I wait for that I.P. address I've been looking up on how to block all websites through the IPCop GUI easily since Mr. Elkner wants to be able to block and unblock websites on the fly. I stumbled upon Advproxy which is another addon for IPCop made by the same people who created Urlfiler so they work together hand in hand. I haven't been able to use it since the test machine isn't ready yet but I've been reading the docs. Apparently it has some Classroom addon so you can group computers together. It can be the whole lab or a few computers and you can choose them based on MAC or IP. Once you've put them in a group and created a password to control that group. You can allow or deny web access with one click. The other cool thing is you don't have to give out the admin password to access IPCop web interface. Instead the teacher would use a different link that takes them to a login page. They enter their password and their groups show up and then they can allow or deny web access.
I believe this should work with the whitelist feature of IPCop but I'm not sure until I can actually work with it.