Aikido is fantastic once you've had five or ten years of serious practice to master it, and some of it's techniques border on magic. So yeah, not likely to be good for high school aged kids.

btw, Aikido is not a nice but ineffective hippy martial art, despite its reputation and philosophy. There are lots of really nasty joint locks. See http://en.wikipedia.org/wiki/Wristlock#Supinating_wristlock for one example - "If performed correctly this technique will break the opponents wrist, elbow and dislocate the shoulder."

The throws can also be pretty brutal ie. throw people face/head first into the ground. Some of the comments on http://www.aikidodemonstration.com/aikido-questions-and-answ... might be worth a read.