They lock you up in a little room with some hideous gorgon-like creature to watch over you. You're not allowed to speak. In fact, the only thing you're allowed to do is homework.
In-school suspension is usually doled out when detention is deemed too lenient and out-of-school suspension too harsh. However, when I found out I was getting in-school suspension, I would usually do something bad enough to bump my punishment up to out of school suspension, which in actuality is much easier.
The person who supervises the students in the "in-school suspension" room at the middle school where I work is a drop dead gorgeous young woman. I suspect that many of the male students who are placed there have an ulterior motive for getting kicked out of class.
BRILLLIANT (read that like the Guinness guys)