Agreed. Don't bother with the theory book.
Go for lesson bk 1 to start your boy with. If it's a little easy, then that'll boost his confidence.
I have the whole set of everything as I've been collecting it for some time. So I use the tech (if they aren't spending much time on scales), and the lesson book.
But...if they are having a problem with a particular skill, I use the performance book. The performance book has extra pieces working in the same order as the lesson book, so they get extra reinforcement of the skill, rather than putting the same piece down again each week.
The lesson book gives the page number for the relevant performance book, and I know that if I turn to that page, there will be nothing extra added. They will have covered everything required already....just that new skill to master. I only lend the performance book.
I also have the midis. I have an acoustic, but also a digital piano. With some of them, if they get the piece well enough, I'll pass it when they can play with the midi. This certainly shows whether they can really do it well. I can change the speeds on the midi which really shows me who is playing in automatic mode. Slow it down and you really have to think.
Less waffle Louise! You only really need the lesson book and if possible the Technique book.
Oh, and one more thing. Those that are really good, get to transpose the pieces. That's fun