The logic behind it:
No one expects workers in a fast food restaurant to flip burgers for free. No one expects teachers to show up and teach without getting paid. But when it comes to kids in school, we think that the distant financial rewards they will earn years or decades later should be enough to motivate them, even though for most kids a month or two feels like an eternity.
A new experiment (pdf) offered kids $20 to do well right before the test began:
The very best results come when we give the students the money before the test, and then we take the money back if they don’t meet the standards. This result is consistent with what psychologists call "loss aversion."
The Dish 