You are forever being bossed around while at school. Parents tell you to attend, your school staff members tell you what to learn, what to eat, what to wear, who to hang out with (and who not to)... the list goes on. It's a lot like prison, apart from the fact that you did nothing wrong. You would expect that since you are coerced to go there and all these things, they would at the very least permit you to browse whatever web sites you will like to when you're held captive there. But, no. The internets are censored, and a great many of web sites are blocked. As luck would have it, there are a few ways of getting around the internet filter at least, and it's a lot more easy than convincing your parents to homeschool you.
An unblocker is like a gateway that sit between your computer and the site you're trying to visit. The unblocker goes to the site you want instead of you, loads 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 visiting sites indirectly. School filters only think you are visiting the unblocker, not the destination site.
Another way of unblocking Facebook at school is by setting up your own unblocker tool. This is harder than using someone else's unblocker but it pays off because if they block it, you can make another. Explaining how to do this is not in this guide, but if you search for "How to make your own proxy" you should find instructions. You can even make some money from letting people use it by putting ads on it.
Other ways to access Facebook are to use translator sites, for example Google Translate or Babelfish. You can also try Google's cached copy of the site. Although, you probably won't be able to to log in that way, so it's still better to use unblockers for Facebook, however these tricks are good with most other sites.