Your school network very likely denies access through their firewalls to the ports necessary for the game, at least from the subnet from which you're accessing the network. There are ways around these types of restrictions, but the 'ethical' answer would be, if you really want to play the game, then you should ask the network admins if they'll allow that traffic through, etc. If they are restricting it, then we can't give you ways around it, as they obviously feel the restrictions are there for a purpose.
(The question was ethical, and you very well may have fully ethical intentions, therefore, I'd suggest asking the admins if they allow, or would be willing to allow, the gaming traffic.)
Good luck with the network admins, and your games.
~ hayabusa ~
"All men can see these tactics whereby I conquer,
but what none can see is the strategy out of which victory is evolved."
- Sun Tzu, 'The Art of War'
OSCE, OSCP (Former - GPEN, C|EH - both expiring / expired)