In 1973, a trio of psychologists convened in a preschool classroom to perform a diabolical experiment upon unsuspecting children. Lepper, Greene, and Nisbett sought to demonstrate that one can take an activity the children naturally enjoyed–namely drawing–and render it hollow and meaningless. More specifically, these scientists hypothesized that if one rewards a human for doing something he or she naturally enjoys, and then remove that external reward, the original intrinsic pleasure will atrophy and perish.

The children were separated into three groups: Group A were promised a handsome certificate of achievement if they would draw during their free-play time. Group B were not informed of the certificate, but they were given one if they opted to draw on their own. The control children of Group C were neither offered nor given any parchment-and-calligraphy tokens of recognition.

The researchers observed, recorded, and rewarded the students. Two weeks later the phychologists reconvened in the observation booth, and found that the children of Group A had lost most of their interest in drawing whereas Groups B and C still illustrated with enthusiasm. This tendency, which has since been supported by additional experimentation, is known as theOverjustification Effect.