An audio editor useful not only to music teachers but also to physics teachers: visualizing sound waves is a treat when explaining amplitude and frequency, among other topics...
"Remove The Lyrics From Most Songs
This will teach you how to remove the vocals from almost any song.
This is great for making your own Karaoke song
Now before i start i want you to know this won't completely remove the singer, but it will do a pretty good job of it so its worth a try."