To Work or Not?

When it comes to launching missiles in the Mommy Wars, Sarah Palin has nothing on Christopher Ruhm. On Thursday, the University of North Carolina, Greenboro, economist published a study showing that kids from high-socioeconomic-status families take a long-term hit when their moms work outside the home—at ages 10 and 11, they perform more poorly on cognitive tests and are also more likely to be overweight than those whose high-status mothers leave the workforce. Children from low-status families, on the other hand, don't seem to suffer as much when their moms work. In fact, many of them do better on the same tests, and they're more fit, than similarly disadvantaged kids with stay-at-home moms.

The findings are surprising, and it's easy to read them as a warning to affluent, educated mothers: if you want the best for your child, don't work. (Conversely, if you're not well-off: get your kid to day care.) But those are dangerous conclusions to draw from the study, and even Ruhm—whose own wife worked while raising their children—says so. "This comes down to a fundamental principle of economics: something has to give. We can't have it all," he says. "But I would never tell anybody what to do or not do about that. I certainly wouldn't tell my wife." So what are women facing a choice between work and home—and those many more for whom work is an economic necessity—supposed to make of these findings?

The study, published in the journal Labour Economics, divided women into two socioeconomic groups, based on several variables (including education levels, income prior to pregnancy, ethnicity and whether a spouse was present at home). The kids from families in the "lower" group generally fared fine if their moms worked for the majority of their childhoods—at ages 10 and 11, they either scored about the same on cognitive tests, or better, than disadvantaged kids whose mothers stayed home. For kids from high-status families, though, the pattern flipped. The more these affluent moms worked—especially if they went back to their jobs while their children were still very young—the less well their kids did on cognitive tests later in childhood. (The high-status children with working moms still did better overall than all the low-status children—so class, not employment, was ultimately the stronger factor in their well-being.)

Why do mothers' choices have such different effects on kids, depending on their socioeconomic situations? Most likely, says Ruhm, the low-status kids get more intellectual stimulation in day care or with other caretakers, such as grandparents, than they do at home. Meanwhile, the high-status kids may find day care less enriching than being with their highly educated mothers. When these moms go back to work, "you're pulling the [high-status] kids out of these really good home environments," says Ruhm, "and a lot of the alternatives just aren't as good."

The same pattern was true of weight: low-status kids weren't any thinner or fatter depending on what their mothers did, but high-status kids with working moms did have a slightly higher risk of being overweight at 10 or 11. The biggest effect on weight came when mothers were working during their high-status children's school years. Maybe, says Ruhm, these moms didn't have time to cook healthy dinners and after-school snacks: "If you're working a lot and you're eating out and buying fatty food, that could have an effect on obesity later in the child's life." Or maybe those kids were left unsupervised more often, and thus had more opportunities to eat cookies in front of the TV—and fewer opportunities to run around outside. "Parents who are working but want to make sure their kids are supervised and safe will often load up the house with sedentary activities, since they can't always be there to take them to sports or to the park," says Karen Eifler, an associate professor of education at the University of Portland. "Their kids are more likely to have a TV or computer and videogames in their room—and also, the higher your economic status, the more likely you are to have those three machines in your house."

Certainly, Ruhm says, there's good reason to think that working women spend less time overall supervising their kids. That's what other studies have shown, and time, of course, is a zero-sum game—there's only so much of it in the day. "Working women do try to preserve the most important activities with their kids. They'll let a lot of things in their own lives go," he says. "But they still have less time to spend. And it's also true that if you're sleeping less and are tired or stressed, that could have an effect on the kids, as well."