Overjustification Effect

Mark Lepper, David Greene, and Richard Nisbett conducted the landmark 1973 experiment testing the "overjustification hypothesis" suggested by self-perception theory. Children who expected rewards for drawing spent 50% less time drawing during free play than unrewarded children. Published in the Journal of Personality and Social Psychology, the study demonstrated that external rewards can undermine intrinsic motivation, with profound implications for education, parenting, and workplace incentive design.