It's probably blocked. You need to find a working proxy, if your school's proxy isn't efficient. Last year, people kept finding proxy sites that would work, and then they'd get blocked, and they'd find more. Shredsauce wasn't blocked, though.
This year I think they updated it and Shredsauce is blocked along with EVERY proxy site.
What I'm saying is that you need to find some obscure proxy site that isn't popular.
this is a wayback machine capture of the site. It might be tricky to install unity (software that the game runs on) on your school computer if there is restrictions, but i guarantee that this site wont be blocked. It is just a cache of the webpage and it hosts the game through the unblocked site.
if your school lets you download another browser, do it. I personally get google chrome and that usually solves any problems for me in regards to blocked websites. My school is fucking retarded and blocked both hotmail and facebook, so now it is virtually impossible to send stuff to yourself without downloading a new browser.
***Looking for beat up XL black or grey saga slims***
Ask one of the big computer nerds, preferably the ones who play magic at lunch or some shit. They probably got a file filled with DOOM and Starcraft squirrelled away in some random program. At least that was the case at my school, usually you cant run any sort of program that's not already on the school computers, but they did some computer wizardry and you could run anything that was in that file. Really glad I made friends with those guys.