One thing that isn’t clear from the new study is whether actual personalities were changing with time — or just behaviors.  

Even though behaviors, such as shyness, appear to change as kids get older, the underlying personality may remain the same, says Jerome Kagan, an emeritus professor of psychology at Harvard University. So someone may remain an introvert on the inside but work at being more outwardly sociable.

An earlier study by Kagan and his colleagues used MRI scans to show that the brains of young adults who were identified as shy when they were toddlers worked differently than those who had been more extroverted as kids.

Kagan faults the new study for not looking at the impact of social class on behavior. Kagan, who has spent a lifetime studying whether personality changes with age, says that a host of factors, including class, can make a huge difference in how kids mature.

Kids from middle- and upper-class homes realize pretty quickly that they are from a privileged class, Kagan says. This gives them confidence. Those from poor and/or blue collar homes may become angry at their starting place in the world and that can lead to more aggression.

Other researchers believe that brain wiring — and hence personality — may actually change depending on what types of experiences people have as they grow up.

It’s quite possible that life events change the brain’s biology, says Rebecca L. Shiner, an associate professor of psychology at Colgate University and an associate editor of the Journal of Personality.

“There may be genuine changes at the biological level,” Shiner says. “We don’t yet know enough about that. The research out there suggests that there is moderate stability to personality by the time we reach age 3, but also that tremendous change occurs even up until the 50s. We need to figure out what causes change.”

Rounding off the 'sharp edges'
Parents should understand that just because kids start out over- or undercontrolling doesn’t mean they can’t succeed in life, says Daniel Hart, a professor of psychology and director of the Center for Children and Childhood Studies at Rutgers University.

By taking the time to teach overcontrolling kids social skills that seem to come naturally to the more resilient ones, parents can help their children overcome, or at least compensate for, shyness, Hart says. In the same way, undercontrollers can be taught to rein in their emotions and be more sensitive to others.

“There are studies that show you can round off the sharp edges of personality,” Hart says.

Linda Carroll is a health and science writer living in New Jersey. Her work has appeared in The New York Times, Newsday, Health magazine and SmartMoney.

MORE FROM PARENTING

Parenting Section Front

Worst nightmare: Babies stolen from their beds   Palin candidacy sparks debate allDay: Palin spark new mommy wars? Government questions plastic bottles' safety Teen suicides dip, but rate remains high Woman saves baby’s life — by e-mail Stressed mothers may raise fat children Ad for nanny: 'My kids are a pain'   Images of the American teen Vaccine-wary parents spark public health worry Parenting Section Front   Add Parenting headlines to your news reader: