You're forever being ordered around at school. Parents and school staff members are saying what you ought to think, who you must and should not be friends with, what you must wear, and even what you should eat. It's a long list. It's a lot like prison, apart from the fact that you didn't do anything wrong. You would expect that since you're being coerced to go there and all that stuff, they would at least permit you to visit whatever websites you would like as long as you're imprisoned there. Apparently not. The internet is censored, a great many of web sites are blocked. As luck would have it, there are many ways to go past that, and it's a lot easier than getting your parents to unschool you.
Unblockers are like a gateway that sit between your computer and the site you're trying to visit. The unblocker accesses the site on your behalf, accesses the page, and sends it off to you. So the site you want to access never sees your IP. So, basically you are browsing websites in an indirect way. School filters only see you accessing the unblocker, not the site you actually want.
Another way of unblocking Facebook in school is to make your own unblocker site. This is more advanced than just using an unblocker but better in the long run because if they block it, you can make another. Explaining how to do this is beyond the scope of this article, if you search for "How to make your own proxy" you will find info. You can even make money from this by letting people advertise on it.
Some other ways to unblock Facebook include to use translator sites, like Google Translate or Babelfish. Also try using Google's cache version of the site. Unfortunately, you probably won't be able to to log in using these methods, so it's still better to use an unblocker for Facebook, though these tips are great for most websites.