Bebot is heaps good.

It is used by Dreamtheater.

Would be cool in class.

Some website has this to say!

Touching the screen causes the robot to move and make sounds controlled by your movements. Play it like a musical instrument, or just have fun watching the robot and making sounds with your fingers.
Features 4-finger multitouch polyphony, multiple synthesis modes, user-definable presets and scales, tweakable synth settings and effects, and more!

Bebot could be used to teach students about synthesisers and scales.