Corporations eager to market their wares to schoolchildren are also getting into the act. Pizza Hut's "Book It!" program rewards kids with a free pizza for reading a certain number of books. McDonald's distributes photo ID cards redeemable for French fries and other goodies to students with good grades and behavior.

Some critics say these extracurricular rewards can turn classrooms into contests, where the prize, not the learning, is the object. Others contend that such enticements reinstate the flawed philosophy of researcher B.F. Skinner, who proved how behavior can be learned by offering food rewards to laboratory animals. This Skinnerian operant conditioning, they say, unfairly manipulates children and turns them into robots.

Stanford University psychology professor Mark Lepper studied the effects of giving children rewards for performing certain activities and found that it leads them to concentrate less on learning and focus more on the prize. He and his colleagues say students actually perform worse in the long run when given tangible or edible rewards.