Desks nailed down? Where are you teaching Stanley? In the 1950's???
Seriously though I am in the same boat as you because my desks are triangular (with the head cut off) in shape and placed in two semi circles, like you would see in a university. It looks cool but for the kids it's not practical at all.
Group works consist of arranging groups to run to certain corners and have them to play the activity or game there. I give a lot of points for good behaviour and for the group that finishes first. I think that will be the key for you because the kids will be difficult to control is they are in difference corners of the room.
Generally I am a bit of a control freak when it comes to group work so I usually arrange a game where they have to play in pairs or threes. A lot easier to control them and also I want to be able to walk around to check them and help out where needed.
Today I will do a review with 5th Grade which will involve placing cards and words on the velcro board and playing a board game of boys vs girls. I have placed in some "back to the start" and "miss a turn" cards and the kids always love it. Of course the winner get some special points!
