Ask HN: Advice for giving private programming lessons?

I've been thinking recently about giving programming lessons in the same way that people give private piano lessons. I was thinking about working with older kids (12+ feels right, but I'm not really sure at what point kids can start really grasping programming) and adults who want to learn. But I don't know what I don't know. My guess is that I should probably have a passing background check handy if I'm working with kids - where do people go for that (there are lots of results on google)? What kind of subject matter do people want to learn (in your experience)? What do I not know that you think I should know?