When I did my student teaching in 2nd grade, the teacher picked one student per week who got to give "clues" at the end of the day... all the kids are dismissed at the same time (it's a reasonably small school), so to get them all lined up, the person of the week (used as another job on the job rotations) gets to give "clues..." If you're wearing green, line up. If you're in Boy Scouts, line up. Stuff like that... if the kids are talking, they'll miss it, and they don't get to line up when their category is called... this works especially well if it's a quiet kid giving the clues and you refuse to repeat them... makes them really listen to each other.