Funny, this is what I do in the Army.
Most likely you're being filtered via a Websense server or Bluecoat. Being it is a school district, I'm going to assume it is a Websense server or similar software solution. Now, if you know routing, web traffic traverses port 80/TCP (HTTP) and port 443/TCP (HTTPS). Usually, these filters only monitor port 80 traffic, while SSL traffic is allowed out. That's why the previous guy said us HTTPS if it is blocked.
Now, you're not going to get past your web content filter, but someone listed a proxy server website here in the chat. That's one way around it, and usually the best. The proxy creates a tunnel from your system to an outside server, by passing all security measures in place from your school, and you virtually "surf" from your outside computer. All traffic is passed back thru the tunnel to your system. Cool thing too is, this traffic is encrypted (IPSEC or ISAKMP), so no one can "see" what you're doing.
I'm a Network Security Engineer in the Army here in Afghanistan, and I'll tell you this...we can see what you're doing because we have the right equipment in place, but I highly doubt your school has the equipment we in DoD purchase.
From a security prospective though, you have to understand this does create a tunnel (or backdoor) into your school network, and the amount of malicious code that is associated with Social Networking Sites...you can cause a major issue at your school, if something were to happen (trojan installed, bot, or something like that).
So just be careful. You can get in some serious trouble if you were to crash a school or district network, and the audits are there, they can find out what happen. It's pretty easy.
Cya!