Just wanted to share that I took a few bass lessons recently with a teacher who taught with a guitar in his hand instead of a bass. Obviously that won't work with a beginner who needs to be shown technique, but I am technically sound and was taking the lesson for theory/musical reasons. I learned a ton about chord inversions, how the bass can cause inversions in "normal" chords, and playing with diminished chords. It's all the type of stuff I had read about, and tried to play with in a band setting, but MAN it really hits home when I'm playing with a teacher who is explaining what's going on and it's nothing but my bass and his guitar - and he would keep playing until I stopped him so I had time to internalize the sounds we were making. Just thought I would post this. Maybe you teachers out there should try a lesson like this, or you students should ask your teacher to use a piano or guitar.