I haven't tried connecting to a school network since I graduated a couple years ago, but my home network with WEP encryption key connects automatically. I think it's just school/work networks where you have an individual username and password that need to be entered in every time.
To the OP, I also found AutoWiFi. Apparently doesn't work flawlessly with 3.0 yet, but still works better then typing in your username and password every time. There's a Lite version in the AppStore so you can try it to see if it works before purchasing.