This thread hits home. I taught folk guitar for years starting about 1968. People came for lessons from someone who taught folk-style flat and finger picking, but often they often didn't have a clue about what they wanted to hear themselves do. The ones who learned fastest, and were really ready to practice were the ones who had songs and tunes in their "mind's ear." I'd get them to bring a recording of a favorite thing...or if they didn't have one, I'd play and sing some goodies with simple chord progressions and work with that. It helped for them to hear the style and energy and techniques, and know THAT's the way they wanted to hear themselves play. Taught a kid who barely had a few chords down to fingerpick after he listened to a recording and asked,"What's he doing?" He just loved the sound he'd heard and was purely motivated to get it right.

After the folk scare, a new problem came along. My students heard rock music on the media and wanted to play that. Well, trad person that I am, I couldn't teach them that music. What they heard on the media was a bag if electronic tricks and miracles that couldn't be reproduced by one individual and one guitar. They'd get turned off by comparing the gentle stuff coming out of their instruments.

Anyway, the main idea of all this, is that I think it's easy to teach someone with above average manual dexterity and a good ear. But anyone who has a clear idea of what he/she wants to sound like, and has had the opportunity to hear a lot of "our" kinda music can be taught to play. Some want it so badly they play all day at home, others are disciplined enough to practice so they get past the hard parts and start having fun. Still others decide they'd rather play sports after school, or really don't want to cut their beautiful, long nails, or think they'll take up the clarinet instead. That's okay, too.