So, you've found that Gmail is blocked? That's unacceptable! As luck would have it, there are ways to get around the school filter and unblock Gmail anyway.
The best way to get access to Gmail at school is to use an unblocking website. You can get onto all other blocked sites with an unblocker. You can find lists of unblocking sites at the bottom of this page.
How do unblockers work?
An unblocker is like a gateway that sit between your computer and the site you want to go to. The unblocker accesses the site you want on your behalf, accesses the page, and forwards it to you. So the site you want to access never sees your IP. So actually you are browsing sites in an indirect way. School filters think you are just visiting the unblocker, not the site you actually want.
A little advice for using unblockers for Gmail
It's best to find an unblocker that hardly anyone knows about. Unblockers that get used a lot will get blocked faster. Most unblockers found by searching the internet will be filtered sooner because they're so obvious. Even if you get a good unblocker it would be smart to have a few others you can use if it gets blocked.
An alternative method of unblocking Gmail at school is by setting up your own unblocker tool. This is more complicated than just using an unblocker but it pays off because if they block it, you can make another. Explaining how to do this is too much effort to explain here, but if you search for "How to make your own proxy" you should find help. You can also earn money from your unblocker by letting people advertise on it.
Some other ways to unblock Gmail include to use translator sites, for example Google Translate or Babelfish. Also try using Google's cache version of the site. Although, you can't to login that way, so it's still better to use an unblocker for Gmail, however these tricks work well for most websites.
More info: Unblock Gmail from school