The amount of time a kid spends in child care, and the quality of that care, could influence academic performance and behavior during adolescence, a new study finds.

Those with high-quality care scored higher on measures of academic and cognitive achievement when they were 15 years old, and were less likely to misbehave, than those with lower-quality child care.

And regardless of care quality, those who spent the greatest number of hours in child care in their first 4.5 years were slightly more likely to be impulsive and take risks at age 15.

While previous studies have found a similar effect, such as a link between child care and IQ, the current study is the first to show the impact is long-lasting, showing up a decade after the child has left the care.

However, the results only show an association, and not a direct cause-effect link. It is also possible that other factors, not measured in the study, were involved.

The study included 1,364 youths who were born in 1991 and who were followed periodically since they were 1 month old. The children were recruited from 10 cities in the United States.

At least once a year until sixth grade, children were evaluated with tests to measure cognitive and academic progress. Parents indicated the type, quantity and quality of child care, while the researchers also observed child-care interactions to evaluate the quality of care, rated on a scale from 1 to 4. High-quality care was characterized by the caregivers' warmth, support, and cognitive stimulation of the children under their care.

Of the children studied, nearly 90 percent spent some time in the care of someone other than their mother by the time they reached 4.5 years of age.

At 15, the children completed tests to assess academic achievement. They also self-evaluated their behavior, with a questionnaire that asked about behavioral problems, such as acting out in class; impulsivity (acting without thinking through the consequences); and risk taking (engaging in behaviors that might harm themselves or others).

Forty percent of the children experienced high-quality or moderately high-quality care. There was a modest link between higher quality care and higher results on cognitive and academic assessments, including reading and math tests. This correlation was similar at age 4.5 and age 15.

"High quality child care appears to provide a small boost to academic performance, perhaps by fostering the early acquisition of school readiness skills," said James A. Griffin, deputy chief of the NICHD Child Development & Behavior Branch of the National Institute of Child Health and Human Development, which funded the research. "Likewise, more time spent in child care may provide a different socialization experience, resulting in slightly more impulsive and risk-taking behaviors in adolescence."

The study's findings were consistent among boys and girls.

The results held even after the researchers accounted for family income, the mother's level of education, and mothers' reports of depression symptoms.

Other environmental factors besides child care have also been found to have effects years later. For instance, one recent study showed a link between how much TV a child watched at age 2 and academic, social and health problems at age 10. 

The new study is published in the May/June issue of the journal Child Development.