The safest way to unblock a website at school is to go to your system technology administrator and have them request the website be unblocked for you.
There are so many blocked websites that what students are able to access via the web is very limited.
I personally would not try to go around the block on my own because that might create problems for you regarding your employment. Two teachers in my school district have been fired over Internet use. I think it is crazy to fire one teacher when there are students, janitors, and administrators who have passwords to the computers. Just don't leave yourself open to any possible problems.