Is there a study that identifies the best cafeteria set up? What size should the tables be? Should there be carpet for noise reduction? Should certain color schemes be used? What kind of lighting is best?
As for the cafeteria tables, carpet etc., there have been studies done on those very issues. You can probably find those articles in educational research journals and magazines. Round tables certainly lend to more conversation and are more conducive to having students sit next to and face others. But the shape of tables, carpet, music -- none of these will make a difference if children aren't taught manners and respect for one another.