I just bought Tom Brown's "Nature and Survival for Children". One thing he suggests is that, to teach young kids the bow drill, you start by giving them the bow, spindle, fireboard and handhold pre-made. If you get them to make their own, they'll get frustrated and give up; if they have a set that works, they're much more likely to succeed. Only after they are proficient with starting fires in this way should they go on to constructing their own set of tools.

This may sound obvious to most of you, but it was a revelation to me. All the books I've ever read on the subject start with a detailed description of how to make the components, and only then described how the tools were used. So I guess I unconsciously assumed that was the way it had to be taught. Brown's method (which was the way his Grandfather taught him) makes so much more sense.