Today as I drove my son home form my parents' house he started talking about how he and his friends were reading Alex Milway's Operation Robot Storm together. It took a few questions and a conversation with my wife to piece together what had happened: he took his copy of the book (which I had read to him a couple of years ago) up to school, and he read it to two of his friends. So now they are reading it together!
When I had gotten the gist of what had happened, I made him an offer: I was willing to help him get two more copies of the book so he can give them to to give to his friends, then they can all read it at the same time and then talk about what they were reading. He took me up on the offer immediately, and the copies are on there way.
And just like that, my son is in his first book club!