Old thread but topic is still relevant.
@nilly,
You found a proxy to bypass a filter which made the math easy or non existant for you, however your actions still leave you liable for accessing the site(s). So IF the school wanted to briing the intrusion to court, they would most likely win.
I am in no way stating what you did was wrong, because everyone should have the right to information. Some websites just do not like individuals accessing content through their own sites, which is why the filters are used in the first place.
This forum for example, will block links, or remove them that lead to sites about game hacking, porn, illegal substances. and other content that is deemed unappropriate to the policies and procedures of the 1up communities operating rules. Offenses would most likely be dealt with by a case by case bases, unless it is a spam account, which would be dealt with abruptly by blocking and added to an IP blacklist of some sort.
Gaining access to the sites that were blocked by the filters of your school, is probably for their interests and yours. The school most likely wants you to get an education out of all things!
Not play video games when you should be learning.