I use these in middle school but would also be fun in elementary school. I like to use groups of four, but I don’t necessarily want them to choose their own seats. I find that this way gives me some control and it gives the impression of "luck of the draw".
They can also be kept and used as a way to call students at random or to do small groups, or literature circle grouping.
If you have never sorted students in this particular way, it is very simple. Group your tables/chairs in whatever fashion you like. Buy a regular deck of UNO cards and tape them to the table. As students walk in hand them one of the smaller cards and they find the corresponding seat.
Good luck and enjoy.