Since its inception in 1991, the largest and longest-running study of American child care has generated plenty of controversial conclusions about the effects on kids of early care outside the family.
The latest findings of the federally funded Early Child Care Research Network are certain to be no exception.
At age 15, according to a study being published today in the journal Child Development, children who spent long hours in day care as preschoolers are more impulsive and more prone to take risks than are teens whose toddler years were spent largely at home.
To be sure, the differences between kids who logged long hours in day care and those who did not were slight. Filling out inventories that measured their impulsiveness, teens rated themselves about 16 percent more rash in their behavior for every additional 10 hours they spent per week in day care as a preschooler.
In terms of risk-taking, the link to time spent in day care was more marginal: 10 more hours a week in day care prompted the average teen to answer one out of 30 questions with an admission of more risky behavior.
But the study's authors defended the findings as significant and even surprising.
For starters, the behavioral differences between day care veterans and those who spent more time in the care of a parent appeared across the income and class spectrum. Those differences were evident even at 15 years of age - more than a decade after Mom or Dad had picked them up at day care for the last time.
And the effects are spread across vast swaths of the population: Some 2.3 million U.S. kids under 5 are cared for at day care centers - about a quarter of preschoolers whose mothers are employed, according to the U.S. census. Another 17 percent, roughly, are in the care of a nonrelative in family day care settings and other, less formal arrangements.
That, says psychologist Jay Belsky, an author of the latest study, makes small behavioral shifts potentially far-reaching, especially as preschoolers mature into adolescence and as peers become the pre-eminent force in a child's life.
In classrooms and peer groups populated by kids who may be just a little more impulsive or risk-taking, "these small effects end up being spread and bounce off each other," said Belsky, a psychology professor at London's Birbeck University. "The dynamic becomes, 'I dare you to take a risk, you dare me to take a risk.'
"Nobody knows what the threshold here is, when the little becomes a lot," he added.
Earlier such warnings have stirred anxiety and guilt among parents - especially mothers, whose large-scale entry into the work force spurred an epochal shift in child care patterns starting in the 1970s.
Deborah Lowe Vandell, the study's lead author, acknowledged that the behavioral effects uncovered among kids with long hours in day care may worry some parents. At the same time, she said, those findings should help parents, as well as child care providers and policymakers, with some guideposts to ensuring better care for their kids.
"We might be much more attentive to issues of helping children in navigating social settings and in teaching them more about behavioral regulation," said Vandell, a professor of educational psychology at the University of California, Irvine.
This and other research suggests that smaller group sizes in day care centers may make it easier for kids to learn important self-control skills, Vandell added.
The experiences of day care may well, with time and a bit of mellowing, prove useful as yesterday's day care denizens turn into tomorrow's workers, said Ellen Galinsky, author of "Mind in the Making" and president of the Families & Work Institute in New York.
"Risk-taking, thinking creatively, taking on a challenge, trying something new - all these aspects of impulsiveness and risk taking can be a positive thing," she said.