Kate,
When lining my students up, I don't count so that they are not "racing". Since I am learning support, I usually call them by classroom. They respond with "lines, lines, lines" while pushing in their chairs and walking. Sometimes I will call just girls/boys or by tables. This seems to work pretty well.
Heather and Annette,
I am jealous about your 3-4 week breaks. We get just over a week for Christmas. Of course, I guess I am finished earlier on June 1. Enjoy your breaks and I believe your students will fall back in place upon returning. That is the beauty of WBT. The structure makes returning easier!