Does anyone have any idea how i can lock or disable the keyboard and mouse on serveral PC's remotely?

A member of staff at the school where i work is trying to find a way of getting the kids to listen to him at the start of class, all they seem to do is come in2 the class room logon to the computers, mess around, ignore him and get no work done.

So the way I look at it if he could lock or disable there keyboards remotely they can do sod all until he enables them or unlocks them!

I have been looking for a while for a solution; so far I have looked at:
Remotely stopping the keyboard and mouse service via a script (I8042PRT.SYS via the Netsvc.exe command)
Disabling the local keyboard and pointer via VNC’s server software, but ever tried to VNC 30 clients at once? It will eat away at network performance
Looked in vain for a utility, which I can install locally and activate remotely

Any help would be very much appreciated,
Thanks in advance