Researchers were acting like big ol' meanies as they gave a group of kids a single marshmallow each, and told them they would get another one if they managed to resist eating the first for 20 minutes. Definitely mean.
The test is a re-run of a famous test conducted back in 1968 which ran 'til 1974 at Stanford University. Groups of four-year olds were given a marshmallow each and were promised they would get another sweet delight if they could manage to restrain themselves from eating the first. Evidently, some could wait, and others had a really hard time restraining themselves.
Interestingly, researchers from the University of Washington and the University of California followed-up with participants from the original tests to further assess the adult benefits of self-control as a child. The researchers assessed the current BMI of the participants, and cross referenced that data with how they performed on the original marshmallow test. They found that each minute a child delayed eating the sugary goodness predicted a 0.2 decrease in adult BMI.