My 15 year old son and I just printed his first black and white images this afternoon. I found an old 35mm SLR on ebay for him and he was interested in printing his first images. They turned out pretty well. I try to give him just enough practical information to get the job done. Not much theory, just the basics he needs to know to do the next step. He's very proud of them.

This seems to be the easiest way to learn. Go out, take the pictures, look at them and decide what would be better next time. The theory is much easier to understand if there is something concrete on hand to examine as a point of reference.