And if you mean within the school, I have an old book from about 95 that lists all the frequencies that they're "licensed" for. They essentially are the "old" business band frequencies. There were also some listed for individual schools but they were mostly incorrect, mine was listed as a UHF freq.
The administrators/security folks/whatever used 151.805MHz at my school (Langley High School in McLean). They were either PL'ed or DPL'ed but I never got a chance to figure it out and they used Motorola HT1000's. Pop in a bunch of freqs in a scanner and just run through them during lunch hour at school or sometime when you'd expect there to be a lot of radio traffic. That's how I found out what mine were using some 6 years ago.