Examines direct incentives for higher grades in primary schools in Ohio, in which students could receive as much as $100. The randomized experiment was designed so that all students in a given grade at a school either were eligible for the incentive, or not. The results showed incentives offered for higher grades increased math scores, but not those of other subjects, such as reading or social science. Can you provide a behavioral economic explanation for this result? Are there any non-behavioral economic explanations that may be at work here?