I've done the whole "secret person" thing for about twelve years, but usually just during May when I'm desperate. It was highly motivational because I would take the student and a friend out to lunch at Subway, Wendy's, whatever was close to the school. It was expensive, yes, but totally worth it. This classroom management strategy seems to be more common now, but I drew a stick every morning and kept it a secret. Throughout the day I'd say things like "I'm looking to see if my person of the day is on task" as I scan the room. Of course, they try to figure out who I'm looking at, but I'm very good at it :) And then at the end of the day I'd say who it was if they made it, or say that the person didn't make it and not reveal the person.
Well, now that I'm at the middle school, I don't have my kids all day and we only have a half-hour lunch. So instead of trying to secretly communicate to each of their teachers who the secret person is that day, I decided to do this by period. Instant gratification. So each period, I draw a stick and a back-up for the class that is currently in my room. If at the end of the period if the secret person has behaved appropriately, he or she gets to choose two items off of my prize line.