What age kids are you thinking of? I started one this past year for my 13 year old and some others of similar ages. I told everyone it was an experiment and I was committing to one book only and then see how it goes.
We read one novel as a group; I made a reading schedule and the kids were to have read to certain points in the book before our next meeting. We gathered once a week for 6 weeks. Parents were welcome to join in if they wanted to read the book too, but so far I’ve had no takers to be part of the discussion group although some are reading at home. At the group, we just discuss the chapters, the characters, themes, conflicts, etc. and I also answer questions they might have. It is very relaxed and low-key and it helps the kids feel more confident asking questions in a group as well as offering their thoughts on the reading.
Everyone enjoyed it, so after a couple months’ break over the holidays, we started up again with our second novel and so far that is going well too. We are doing it in the same format (except this book is a little longer so we will meet for a few extra weeks). Again, I am just committing to one book at a time, but if things keep going this way, we’ll probably continue (again, probably with some time off between books).