Love these for teaching purposes. They work a bit like choir chimes or handbells; every kid gets one and only plays it when their pitch comes round in the song. If you want to get fancy, you can also get the chromatic set that will give you the "black keys" on the piano. Boomwhacker also makes caps to fit over the ends of the tubes that will lower the sound by an octave; I found that the kids like the deeper sound and find it easier to distinguish pitch. You can hit two or more together to make a chord; you can play them with mallets for a different timbre; they're near on impossible to break. Perfect.
A note to other music teachers: the notation software Sibelius has a feature that will color in noteheads in Boomwhacker colors. Very, very handy. And they're getting more popular, so there are lots of materials available for them if you don't want to write your own, some with accompaniment CDs. I recommend getting enough sets so that the kids don't have to take turns and dividing them into groups by pitch; they're braver when they have a buddy.