PSTools allows you to execute one command for a file full of IP addresses or computer names. A command could be as follows.
C:\PStools\>psshutdown @C:\PStools\computers.txt -s
.jpg)
This would execute a shutdown command on each computer inside the file specified (C:\PStools\computers.txt). If there is no luck, your IT Administrator has probably set up a Domain account to control every computer in the school. To crack this, an OPH-Crack Live CD may be used, or OccupyTheWeb's Hack Like a Pro blog on Windows Password Hash Cracking. PSTools has a range of commands, from Stopping/Starting services to Shutting down computers to even establishing a remote Command Line.
Hope you find what you are looking for.
.gif "hack school computer")
Password - sujay