"Parents who have these babies who are hard to deal with can become very discouraged," said lead researcher Anne Dopkins Stright, an educational psychologist at the University of Indiana.

The study concluded difficult infants respond more to both good and bad parenting than laid-back babies, who are not as affected one way or the other. With bad parenting, the difficult babies more easily derailed. With good parenting, they shine, the study found.

"I would have predicted that if you did a really great job parenting your child, the easy babies are going to be the ones who really do well, but that's not what we found."