Teach the kids a simple and short song like "London Bridge is Falling Down" (first song that came to my head - maybe repeat the first verse) and teach them that everytime the students hear this song they have to get up and move their desks into a certain order. It will take you some time to get them to do this (probably 5 or 6 times at least) but when they have it off you will never have a problem with them moving their desks then
