Kids, Genes and Daycare

You can always count on studies of daycare to scare the living daylights out of parents, especially when they find that the more hours kids spend in daycare the more likely they are to be aggressive (a conclusion that, critics said, reflected shortcomings in the study) and that poor-quality daycare can hinder kids’ cognitive development, as the original report of a long-running study and a more user-friendly write-up both note.

These findings and more have emerged from the longest-running and most comprehensive study of daycare, the Study of Early Child Care and Youth Development, which the National Institute of Child Health and Human Development began in 1991. But there has always been something funny about these findings, namely, the small size of the effect of daycare. It raises the possibility that daycare does have strong effects on kids, but that the effects differ depending on the child, with the result that when you take an average over thousands of kids in a study you wash out the individual effects.

Psychologist Jay Belsky suspects something like that is going on. Now at Birkbeck College in London (he also blogs for Psychology Today), he suggests that children have what he calls a “differential susceptibility” to their environment, including the environment called childcare. (I wrote about his work in a story on how children’s genetic differences affect how they’ll respond to various forms of parenting, such as learning from mistakes.) According to this model, the reason studies don’t find a greater effect of child care is that they mix apples and oranges: the apples are children who are susceptible to the effects of daycare and the oranges are children who are not. As Belsky and colleague Michael Pluess put it in a paper in the April issue of the Journal of Child Psychology and Psychiatry, “Inconsistencies regarding developmental effects of non-maternal childcare may be caused by neglecting the possibility that children are differentially susceptible towards such experiences.”

Using the NICHD data, they therefore looked for relationships between a child’s temperament (which is under at least partial genetic control), childcare and outcomes when the children were about four-and-a-half. Their conclusion: “children with difficult temperaments as infants exhibited both more behavior problems when faced with low quality care and fewer when experiencing high quality care than children with easy temperaments.” These difficult children—hard to soothe, cranky, sensitive—really feel the effects of daycare, for good or ill. That doesn’t mean you shouldn’t put such a child in daycare. Look carefully at the last part of the quote above. Although these “negatively-emotional infants” are apt to emerge from poor-quality daycare at age 5 with more social and behavioral problems that children not in daycare, they have fewer such problems than the stay-at-home kids when they receive high-quality daycare. Mellower children are like Teflon: the effects of daycare, of high or low quality, simply do not stick to them as much.

Message: know your child. Know your daycare.