The finding surprised them because, at least in popular lore, parents supposedly spend more time with boys than girls. And Baker says that perception does tend to hold true for older children — fathers tend to spend more time with boys once they are older than age 4 or 5. When children are smaller, Baker says, parents spend about the same total time with boys as they do with girls.
But the striking difference comes in the sorts of activities the parents said they engage the kids in. The survey data suggests that young girls are more likely to be taken to libraries than are boys, are more likely to own books than are boys, and are more likely to be read to for longer periods of time than boys.
The economists focused their analysis, recently published by the National Bureau of Economic Research, on first-born children in order to get at the disparity in parental investment. It would have muddied the waters to compare parents caring for an only child with parents caring for their second or third child, Baker says. But they did find that the disparity also shows up clearly among fraternal twins. Here again, the parents surveyed seemed to devote more time to girls when it came to cognitive activities.
Since parents say they spend the same amount of time overall with boys and girls, Baker's analysis suggests that if parents are spending more time with girls on cognitive activities, they must be spending more time with boys on other kinds of activities. While it's possible to speculate that those activities involve more active play, Baker says the surveys could not provide a definite answer.
The big question, of course, is why these disparities in parental investment come about at all. After all, as Baker notes, many parents are familiar with research showing that elementary school boys trail girls in test of vocabulary and math. And they've also likely heard about studies suggesting that early interventions might have a big impact on the lives of children.
Milligan says the short answer is that no one knows why parents spend more time with girls on cognitive activities. One theory holds that girls might have a greater inclination toward such activities. (Theories suggesting innate differences between boys and girls and between men and women are hotly debated.) Another theory is that parents may be following cultural scripts and unconscious biases that suggest they should read with their daughters, and have active play with sons.
It is also possible, Baker says, that the costs of investing in cognitive activities is different when it comes to boys and girls. As an economist, he isn't referring to cost in the sense of cash; he means cost in the sense of effort.
"It is just more costly to provide a unit of reading to a boy than to a girl because the boy doesn't sit still, you know, doesn't pay attention," he says, "these sorts of things."