What would happen if you paid your kids to get along?

From NPR's "This American Life":
"Lisa LaBorde has two daughters, and having grown up an only child, she can't understand why they fight all the time.... Lisa decides to enlist the aid of science to see if she can turn these enemies into friends, in just a month." So Lisa paid the older sister, who was 12, $100 to play with her four-year-old little sister every day for a month. Her theory was that the positive attention from her older sister would reduce the younger sister's inclination to annoy her older sister...she called it the "Kill Her With Kindness Experiment." She recorded the number of times she needed to intervene in the kids' fighting. After a month, she found that the kids were indeed fighting less...but also realized that her constant intervention had been part of the problem.

You can hear the whole story (18 minutes), including clips of the kids' interaction and some reflection on whether it makes sense to pay siblings to be nice to one another (!), at This American Life. Click on "Complete archives," then on the show for November 10, 2006 (David and Goliath).