As I remember there were lots of discussions about using the Pi as a thin client I can confirm rdesktop works great from the default debian install. I'm actually writing this on a rdp session from my Pi to my Win7 box! To install rdesktop all you need to do is from a terminal session;
sudo apt-get install rdesktop
Once installed;
rdesktop {hostname/ip address of Windows machine}
I'm not sure if this is a duplicate but I couldn't find any other postings. This should give schools even more options now just have to come up with a decent bootmanager.
Rob