In the paper that we're describing, but he gave them pennies or candies after they got one right. And then he found that later on, these kids worked harder. His theory of learned industriousness is about you are interpreting that feeling of fatigue in a way which is different than what you did before reading this paper. If we know that students in low income schools tend to do much worse with cognitive endurance, i wouldn't be shocked to learn that there's less emphasis and less resources for physical activity in those schools.