Another way to group is by colors and numbers. We also use Power Teaching, so when students are asked to teach each other what they just learned, I may say 1s turn to a 2 or odds find an even. I can also ask for all my ones to group together or all my greens to group together. This is just a way of getting them out of their desks and learning to work with other students they may not generally flock to.
-Mrs. Cardiel. :)