I usually always start my students off in small groups of 4-5. This year, I am going to do something different. I'm putting two desks together side by side for the first few days/weeks of school until I have taught all important procedures. then, I will probably move them to small groups. By the way, I change my groupings at least once every 9 weeks or more. I like to give my students many opportunities to work with as many different students and personalities as possible.

ps. When I taught fourth/fifth grade, I started my students off in the U shape and then moved them into small cooperative groups. It worked out very well.