You are constantly being told what to do while in school. Parents and teachers are saying what you should think, which students you should and shouldn't go out with, what you must wear, and even what you must eat. It's a long list. You'd swear you're in prison. You'd expect that since you are forced to go there and all these things, they'd at least let you visit any web sites you'd like as long as you're there. Well, no. The interwebs are censored, and a great deal of web sites are blocked. However, there are a couple of ways to go past the restrictions, and it's a lot more easy than convincing your parents to unschool you.
An unblocker is a kind of gateway that work between the computer you're on and the site you want to go to. The unblocker goes to the site you want on your behalf, accesses the page, and sends it on to you. So the site you want to be on only sees the unblocker's IP. So, basically you are visiting websites indirectly. Internet filters only see you visiting the unblocker, not the real site.
Another way of unblocking Facebook at school is by making your own unblocker tool. This is more complicated than just using an unblocker but better in the long run because you can make more of them. How to do this is not in this guide, do a search for "How to make your own proxy" you should find instructions. You can even make money from letting people use it by letting people advertise on it.
Other ways to access Facebook are to use translator sites, such as Google Translate or Babelfish. You can also try Google's cached copy of the site. However, it won't let you to log in using these methods, so it's still best to use unblockers for Facebook, however these tricks are good for most other sites.