The study, published in Child Development, suggests infants with more sensitive nervous systems are more likely to be termed difficult, but they are also more sensitive to excellent parenting and harmed more by poor parenting.

Researchers from Indiana University Bloomington and the University of North Carolina at Chapel Hill tracked children from l,364 families, part of the National Institute of Child Health and Human Development Study of Early Child Care.

Mothers completed questionnaires on their six-month-old babies' temperament. Children who did not respond well to new situations and people, were very active, had intense emotions, cried a lot, and did not adapt well were classified as having difficult temperaments. The researchers observed mothers' parenting six times from infancy to first grade.

Lead study author Anne Dopkins Stright of Indiana University Bloomington Children said infants who are exhausted and frustrated often become more academically competent and socially skilled students in the first grade compared to infants who were easier to parent.

"The key to first-grade adjustment for both difficult and easy infants was good parenting," Stright says in a statement.