Everyone's always ordering you around while in school. Your parents tell you to attend, the teachers tell you what to write, what to eat, what to wear, who to spend time with... the list goes on. It's a lot as if you're a felon or something like that. You would think that since you're forced to go to class and all that stuff, they would at the very least be nice enough allow you to browse any sites you like while you are held captive there. Alas, that is not the case. The interwebs are censored, a great deal of sites are blocked. Fortunately, there are a few ways of getting past that, and it's very much more easy than getting your parents to unschool you.
Unblockers are like a gateway that sit between your computer and the site you want to go to. The unblocker goes to the site on your behalf, accesses the page, and sends it on to you. So the site you're trying to visit only sees the unblocker's IP. So actually you are surfing sites indirectly. School firewalls only see you visiting the unblocker, not the site you actually want.
An alternative method of unblocking Facebook in school is to set up your own unblocker tool. This is more complicated than using an unblocker but it's a lot nicer to have because you can make more of them. Explaining how to do this is beyond the scope of this article, but if you search for "How to make your own proxy" you should find help. You can even make some money from this by putting ads on it.
Some other ways to unblock Facebook include to use sites that translate pages, such as Google Translate or Babelfish. You can also try using Google's cache version of the site. Unfortunately, it won't let you to login that way, so it's still better to use unblockers for Facebook, however these tricks work well for most other sites.