My kids write in their writing notebooks every day. Sometimes they are writing to a prompt, and sometimes it is just random free writing. On Fridays, they take their notebooks with them to their writing club. I assign every group. I usually mix it up based on ability, but I REALLY try to get my higher kids in the same group because they need that support from one another. I also don't want them "running the show" and doing all the work in the group while the other kids just sit and listen.
Writing clubs last about 30-40 minutes depending on how much time we have. Each student in the group gets about 10 minutes to share their favorite piece they wrote that week. First, they read it out loud to the group for enjoyment. When they are finished reading, the kids in the group talk about it. They talk about what they liked, if something didn't make sense, things they could add, things they could fix, etc. It's AWESOME. Many times the kids help with spelling and punctuation mistakes as well. I'm amazed at the wonderful conversations my kids can have. It's a great support group, and the kids love it.
I made up this worksheet to go with the groups to make sure there was some kind of accountability. There will always be that group that just wants to play, and you have to constantly redirect them. This page helps them stay on task. You can get this for FREE in my TpT store HERE.