That's the finding from a new study by scientists at Pennsylvania State University, New York University, and the University of North Carolina at Chapel Hill. The study appears in the journal Child Development.

A group of cognitive processes called executive functions are considered important for regulating behavior, managing new and potentially confusing information, adjusting to school, and making academic progress in the early elementary grades. We know that executive functions develop rapidly in early childhood, and that they're compromised by stress. Researchers in this study asked whether or not executive functions in early childhood are influenced by stress in children's lives.

Looking at almost 1,300 young children in mostly low-income homes, they examined aspects of children's early environment between 7 and 24 months, including demographic characteristics, the household environment (such as safety and noise levels), and the quality of parenting (for example, levels of mothers' sensitivity, detachment, and intrusiveness when interacting with their children). They also examined one indicator of stress -- by measuring levels of cortisol, the stress hormone, in the children -- and administered a battery of three tests related to executive functions when the children were 3.

The researchers found that children in lower-income homes received less positive parenting and had higher levels of cortisol in their first two years than children in slightly better- off homes. Cortisol was higher in African American children than in White children. Higher levels of cortisol were associated with lower levels of executive function abilities.

"In sum, early stresses in the lives of children living in poverty affect how these children develop executive functions that are important for school readiness," explains Clancy Blair, professor of applied psychology at New York University, who led the study.

The study was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the National Institute on Drug Abuse.

Note: If no author is given, the source is cited instead.

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