Is "Content Barrier" still around?
Hey, Tom--
I don't deal with Macs much, nor do my kids' schools anymore. This exchange at macintouch.com concerning Kidsafe and Cyberpatrol refers to a Mac-compatible product called "Content Barrier". It's a Q&A format, so you can always ask them to point you at another alternative filter if Content Barrier has also bitten the dust.
The schools around here use Bess, but I notice that's only for a Windows platform, too.
Good luck!
Regards--
Mary Anne