Every time a new proxy appears, the blocking software suppliers discover it and send automatic updates to the schools, etc. This will require a more sophisticated solution, perhaps similar to the frequency hopping or spread spectrum anti-jamming techniques invented by Hedy Lamarr:http://en.wikipedia.org/wiki/Hedy_Lamarr
In some kinds of secure (encrypted) communications, the key for the next set of exchanges is included in a transmission. A similar thing could be done with proxy domain names. The proxy could change its own domain name to a random string on a periodic basis, automatically register that new name, and broadcast notification (encrypted) to registered subscribers. The name change would occur too quickly for proxy blocker software updates to be installed.
This technique is not patentable because I, the inventor, declare it to be public domain.