When I am absent, I ask the guest teacher to rate each class on a scale of 1-6, with 6 being an outstanding score. If a class receives a rating of 5 or 6, I provide verbal praise and a treat when I return. My students are aware of the system and what it takes to earn an outstanding score. Most of the time the students do score well. I call substitutes 'guest teachers' and I discuss with the kids how one treats a guest. So far, so good.