To visit blocked sites at school could you just not take a portable instillation of firefox on a memory stick and configure that to use a http proxy server e.g. 127.0.0.1 port 8080? That would be simpler than using a proxy website and the school couldn't block you then.
I remember a while back my school blocked NGU. Since I'm on good grounds with the tech staff I asked if they could unblock it, next day it was :megusta:
proxy sites can be traced on google yes some time they blocked the proxy sites as well but there are a lot of new site which can easily allow u to bypass the all kind of trafic........