We do this thing we call "Spot Games" at my school. During a regular work day while the whole crew is moving around on stage, we have the spot-ops follow random techs around the stage. Some of the older kids really get into, and will start running around, doing action-rolls and what not to keep the kid on their toes. It seems to help. Within a half hour they can
iris up or down rather fast depending on the person's location on the stage, and will know when to fade out or let the other spot-op pick up the target.