[Oni]

What difference would connecting to an ethernet outlet make? You could get more done by intercepting packets that are using a wireless connection. Unless this port is special and can bypass restrictions set by a network administrator, the ethernet outlet is meaningless.

Whatever you do, I wouldn't bring a Mini PC to your school so that you can hookup to an ethernet port where you probably shouldn't be.

You should also be weighing the consequences of what you're doing. Is what you're doing even worth getting caught over?

Inclined to agree. I recommend doing some reading about the "Wifi Pineapple". If it worked for me 10+ years ago, I'm sure it has some uses now.

I don't have a Pi anymore, but upon searching there's now a number of solutions for sniffing on a Pi. "Pumpkin Pi" seems to be one of those solutions.