Eh, just some advice to not get blocked. Take any and all mention of 'proxy' or 'filter' out of the web page. I know it'll make getting your proxy well-known a little harder, but it'll get blocked less. School filters often look for keywords such as the ones I've said and when they find them they'll block 'em.

Also, if you're using a commonly found proxy script, you'll wanna obfuscate the code a little, maybe stick in a few <!-- comments --> in places. School filters check for blocks of code sometimes and the comments may throw them off.

If all else fails, take your source code, convert it all to Base64 using any old online converter, and use PHP's base64_decode function, like so:
[PHP]echo base64_decode(YOURBASE64STUFFHERE);[/PHP]