I was one of the kids in that experiment. I was tested in 5th grade in nearby Mt. View (so was Steve Jobs, who was a year behind me). We figured out quickly what was going on: The bus they tested us in had a ‘mirror’ behind us that was, in fact, one-way glass . . .so we knew we were part of an experiment. Word got around quickly among us that we would get more stuff if we deferred the reward. The grad student testers must have been very impressed that we were all willing to wait a day to get a better gift (not a marshmallow, but a cool eraser, If I remember correctly). So much for child development research . . .
That’s interesting! :)