We have a boy's and a girl's bathroom right outside our doorway. To prevent a line, I made a sign for the boy's and the girl's bathroom. One side is red and the other green. They are attached to the wall by the doorway with velcro. When a student needs to use the bathroom, they look to see if the sign is green. If it is, they turn the sign over to red, use the bathroom, then turn the sign to green when they are no longer using the bathroom.