If you choose the books one at a time, you can always soothe hurt feelings by promising to put popular non-winners back into the pool for the next vote. It is also a good idea to involve members in planning the rules of decorum. That way they will feel more invested in showing respect for one another during book discussion. A leader's job is to be the guide on the side, not the sage on the stage. Never shame or scold anyone into reading, but do ask participants to set goals for themselves as readers.
Leaders can model goal setting by sharing their own reading goals with the kids.
Book group is not the place for participants to get hung up on vocabulary, the way they might in school. Admit to them that adults don't always know all the words either, and that it's okay not to run to the dictionary every time they come to an unfamiliar word. Reading the first chapter with participants before they leave is a good way to get them off to a confident start. You may also want to send them home with Post-It notes or reusable tape with colored ends, so they can mark passages they like or have questions about as they read. Have Few Rules, Lots of Open-Ended Questions, a Break, and a Snack Groups generally meet weekly for about an hour, anywhere from four to ten weeks, according to time available and motivation.