Classroom Management

Over the past ten years of teaching second grade, I have learned some tricks for keeping harmony in my classroom.  One of the best ideas I have implemented is called "mystery student."  Whenever we have to go to a special or take a bathroom break, I pick a mystery student.  All of the students have a number on a Popsicle stick (according to their ABC order).  Before we leave the room I pick one of the sticks.  Since they don't know whose number I picked, they all have to behave.  When we return to to the room, I share with the students whether the student was successful or not. This would mean that the student followed all the rules for passing in the hall.  If he or she was successful, they would get to pick out of my prize box.  If not successful, then I simply say that our mystery student was not successful, and I don't reveal who it was.   What ideas do you have for keeping a harmonious classroom?