Helping Kids Learn Discussion Etiquette

I'm finding it challenging to help my seventh graders learn to discuss in their Lit Circle groups. We have the same problem with whole-class discussions: everyone starts talking at once - as a friend put it so well recently about a conversation on an email group: "Everyone wants to be heard but nobody wants to listen." One thing that has helped there has been having students write down their ideas before a whole-class discussion. When it comes to Lit Circles, the kids have prepared the selection and each has had a specific role, so that they are theoretically showing up with something to say, and not just inventing something on the spot. Of course, several came unprepared, so that didn't help.

I'm still working on this and I'm open to helpful hints. Here are some links I found:

Teaching Kids to Discuss.

Making Discussions Work.

Discussion Skills. (For older students, but some good ideas.)