Hi there!
I think you have two options. You can go for the Teaching challenging teens. It explains the method in a story-like way, it is easy to read and you will find extensive information about the method.
Or, you could go for the training manual. It is shorter (and less extensive) than the first one and it is more oriented into training new teachers in WBT.
Another option you have (not related to books), would be attending one of the training sessions that Biffle, Vanderfin, Rekstad and company give out for free. I think this last option is, no doubt, the best if you live somewhere near one of those events.
Best,
Edward