Several folks have mentioned liking thicker rope for teaching knots. On the other end of the spectrum, what about paracord? It's not too pricey if you're handing it out to groups, and what I have found is that I EDC a length in my pocket, which is comfortable in the pocket, and I always have something to practice with. Plus it doesn't unravel and it holds up over time. That might encourage the scouts to keep it with them to practice. The only drawback I've found is that if I'm working on a knot over and over, it starts to rub my fingers raw...I don't know if that happens with other rope/cord.

I agree that practice (along with a practical use) is most important. I had a kid a couple of weeks ago in a martial arts class just learning how to fall. He did the fall a few times and then stopped. I told him to keep working and he said, "I did it five times, I know it." Like one of the SAS books says, you have to know how to tie the knot so well that you can do it in the dark, with numb, shaking hands, because your life just may depend on it.

With music, martial arts, knot tying, whatever...I feel that if I have to think about what I'm doing, then I don't know it well enough yet. That is a hard concept for kids to understand.