By creating categories for each group, and then insuring that your students apply those categories to their posts as they go up, you can make it easy for students to locate and interact with the the work of their groupmates.
To create categories, go into the Dashboard, and click on the Posts->Categories menu.
Then, create your categories. When your students write their posts, they will show up on the right side of the post editor. Be sure to remind students to select the appropriate category for their group!
You’ll also need to make sure that navigation exists to the category archive for each group. You can add this in a variety of places — but the two best are via a custom menu and via adding a category widget to the sidebar of your site.