My school blocks sooo many sites its not funny. Even Wikipedia. Why? I don't know.
One way to get past a filter is to just type the ip adress of the site that you are trying to get on. If you don't know the ip adress, go to command prompt and type "ping www.sitename.com" It should return a message saying "pinging (a bunch of numbers here) with however many bytes of data. That bunch of numbers is the ip address.
Next up, proxies. I know one completly unblockable proxy, but it is loaded with pop-ups and I dont like it much.. You have to type this EXACT address or it will not work. It is "https://vtunnel.com/"
Another way is to use an internet gateway. Like Ipig. I pig isn't free though. >.< Or you could use a VPN (again, not free...) You also could Create a vpn if you have an extra computer at your house, but i've never tried it.
The vpn or internet gateway works best.
I say try to use the ip address, or look for a good proxy. Or just search on google for ways to get past filters. Thats how I found all this stuff.
Sorry if I wasn't very clear, hope this helps.