NO MORE MESSY WHITEBOARDS. After a few years of picking up tissue off of my floor and nearly choking to death on even the "low odor" dry erase markers, I have finally found a solution to my problem. I was using the dry erase markers for standardized test practice so that students could show me their lettered answer and I could quickly see who "got it".
With these cards, printed front and back on 3x5 plain index cards and laminated, I can simple look out and in less time than they could ever write, I check for understanding. The letters are color coded, so if you look out and see a red mixed in with your see of blue, it is easy to see who doesn't understand.
Time saver and a cheap alternative to white boards!