Bribing the kids

New research offers guiding principles for using rewards to shape behavior

Scientists have worked out a set of guiding principles for using rewards to shape behavior. I’ve tested them in my own home — they are shockingly effective. And I’ve become convinced that, more widely applied, they could make the world a happier, healthier place.

That’s a big claim, but let’s start with carrots. British scientist Jane Wardle and her colleagues recently tackled the age-old question of how to encourage kids to eat their vegetables. She recruited hundreds of 4- to 6-year-olds, and asked each to taste six vegetables, including carrots, celery, and cabbage. She had the children rank them, and selected each kid’s “target’’ veggie from the bottom half of their list.

Over the course of two weeks, Wardle compared doing nothing with three different strategies. One was simply asking the kids to try the vegetable. In another, the kids were lavishly praised (“Brilliant, you’re a great taster!’’) And in the third, the kids were offered a small reward (a sticker) for their efforts.

The rewards, according to a recent write-up in Psychological Science, enticed kids to try the vegetable more. But the big surprise is that, three months later, the sticker kids were still eating substantially more of it. (The praised kids also ate more, though not as much.) This is a key insight into human behavior: Temporary rewards can bring permanent change.

Wardle’s second finding has implications that might not be immediately apparent: the kids came to truly like their vegetable. This runs counter to decades of influential research in psychology and economics suggesting material rewards can backfire, undermining a person’s “intrinsic motivation.’’ But Wardle’s result did not surprise University of Alberta professor David Pierce, who has analyzed nearly 150 studies on motivation and concluded that the backlash is easily avoided.

Based on what is now known, Pierce and others suggest a set of guiding principles.

Choose a specific, positive behavior. “Have at least three bites of a vegetable every dinner for a week.’’ (Good.) “Don’t annoy me.’’ (Not good.)

Choose smart rewards. Work with your kid to choose the prize, investing them and ensuring it’s one they truly desire. A few selections from the LEGO catalogue were all it took me to solve an Olympian parenting problem: thumb sucking. But a reward need not be large.

Stay positive. In our house, we call them “challenges.’’ It is not about “fixing’’ a negative. Don’t nag. Let it be their choice. Pile on the praise.

Small steps first. Faced with an overwhelming task, start with easy goals, and small rewards, and slowly build. So, you might start with “avoid thumb one day between breakfast and nap.’’ Consider a detailed progress chart.

We are not robots. The research warns that material rewards can sap creativity, or backfire if someone is already quite interested in a task, or motivated by idealism. Hopefully you can inspire your young scholar with the thrill of learning, rather than paying for grades.

But what caught me off guard were the positive side effects. Getting my 4-year-old ready in the morning had become an exhausting, defiant drama until I introduced a series of rewards over a few weeks. In short order, he changed from a model of opposition into a little boy who revels in the sheer joy of doing things for himself. Replace a negative habit with a positive one, and it sticks because it feels better.

These are not just insights for parents. For example, Harvard Business School professor Teresa Amabile writes in the new Harvard Business Review that incremental progress — she calls it “the progress principle’’ — is profoundly underappreciated at work, and can foster jumps in productivity and creativity. She also tells me she dropped 15 pounds by buying herself (non-food) prizes as she hit milestones.

Think how much you might accomplish if you could get the incentives right. More importantly, imagine how much of what we hope for in the world — for our children, for our society — could be realized if we found ways to kindle the motivation.

Gareth Cook can be reached at cook@globe.com or Twitter @garethideas.