Does it support midi-in? I've got a small midi keyboard, being able to hook that up to this would be ideal.

And if that's in there, what about a mode - like typing instructors - where the page only advances if you hit the right keys? I think that would be an ideal way to learn the notes, followed by a mode like Guitar Hero where you have to hit the right notes at the right time.

Finally, given that the app is aimed at teaching, I'd add a progression path, have the user start with simple music and gradually progress. Finding rights-free midi files and assessing difficulty might be difficult though.