The book teaches by example. I'm a big believer in lots of simple code examples (and making sure they all compile!).
There's an interesting essay by Peter Norvig that says it takes 10 years to teach yourself a programming language:
I think more highly than he does of the Teach Yourself X in 24 Hours (or 21 Days) concept, naturally, but there's a concept in his essay that I've used to motivate my kids. It's the idea that it takes 10,000 hours of practice and effort to be great at something. I told my kids they'll never have more time to become great at something than when they are in their teens. My oldest son is devoting himself to becoming an animator. When I was his age I was writing software (mostly BBSes) on my Commodore 64.
The goal of the 24 Hours book is to leave no beginners behind. A reader who spends 24 one-hour sessions with the book will progress through the fundamentals of the language by creating working programs and writing some of their own.