In our classes, students typically work in groups. We use name tags made of index cards to flexibly group students. We ask students to drop off their name tags at the end of class and place them at the beginning of the following class. This allows us to make strategic choices about who we'd like to work with whom for each particular class. Depending on the audience and our goals, this may include placing them at random, grouping by level, or across levels, or to place all the slackers at the same table, or to separate chatty friends. It's important to start the new groupings right away. Otherwise, students may strongly resist our attempts to break up settled groups. Having group tables is helpful but you can also ask students to rearrange their seats to form a small group. If you do this consistently from the start of the semester, student take it on as a class routine.