Ask your school's IT department to extend wireless
coverage to the area you want.

You can also get an external antenna or an external
wireless receiver but that is going to be clunky
carrying it around with your laptop.
I'm sure google can help too.

Finally if you can afford it, cellular carriers
offer internet access so you can get Internet
wherever there is a cellular phone signal. But
this is costly and slower: $30-$100/month

Depending on your school some classrooms might be
hard-wired so you can plug in a network cable.