Three Finger Rule: "I Am Done"

In my classroom my students know that when they are done with the task I have assigned them (such as writing their name on their paper and then to wait for further instructions) that they are supposed to put three fingers in the air. I tell them that each finger represents one word: "I" "am" "done". This way I don't have 25 students telling me every 3 seconds that they're done and waiting for me and I can quickly see who's ready to move on and who is not. It works great!