But here's the kicker. As a final part of the experiment, Dweck had all the kids write out their thoughts about the test, ostensibly for other kids who would be taking it in the future. There was also a space for them to write in their scores. Nearly 40 percent of the kids who had earlier been praised for their raw talent lied about how well they had done on the test. They inflated their scores. They were in effect using lying as a way to deny their imperfections, which had become shameful to them.

Dweck has also made ordinary kids vengeful, insecure and lazy—all by molding their core beliefs about themselves and their potential. She describes these experiments and others in her book "Mindset: The New Psychology of Success." But don't be alarmed. These undesirable personality traits aren't permanent or irreversible. Indeed, in more recent work Dweck has actually intervened to change kids' beliefs for the better. One such intervention, reported in the most recent issue of the journal Child Development, helped teenagers make the difficult transition to higher-level mathematics by altering their beliefs about effort and achievement.

In this five-year study, Dweck first examined how seventh-graders' beliefs were affecting their success in junior-high-school math, without any intervention. Adolescence is a tough transition for many kids for a lot of reasons, and gatekeeper courses like algebra and trig often sort out the high achievers from the also-rans. The kids had all arrived at adolescence with beliefs formed from years of parenting and formal education. Dweck found, as her theory would predict, that kids with a "growth" mindset improved their grades over two years, while the performance of kids with a "fixed" mindset stayed flat.

Then she gave some of the kids an added advantage. She had all the kids take an eight-week study-skills course, but half the kids were also introduced to the most recent neuroscience on the brain's malleability. They learned that the brain is a muscle, which like any muscle can be strengthened through hard work. They were in effect being taught to believe in the human potential for growth, though it was disguised in research papers on sprouting neurons and synapses.

What happened? First, the kids who were taught about human potential were much more highly motivated as math students than their classmates who did not get the neuroscience lessons. What's more, those with a newly acquired belief in effort and growth had better grades than those who were still stuck in the belief that temperament and ability are fixed. They believed that they could flex their intellectual muscles, so they did, and the effort showed up in their achievements.

Old beliefs die hard. And the belief in natural talent and destiny is deeply entrenched. But the clear message from psychological research is that even core beliefs can be changed, and changing belief, in turn, changes personality. Those kids in Dweck's earlier study aren't incorrigible liars and scoundrels, at least not yet. That will depend a lot on their parents and teachers.