If you want your kids to be smarter – then try spacing them two years (or more) apart

But if you want to produce good-looking offspring, maybe you should try something else.

So you want your kids to be brighter than everybody else’s brats?

Don’t we all.

Or rather (in the case of the Grumbles) we once did – nowadays we are a bit past bringing new generations of Kiwis into the world.

So this post is for younger constituents.

If they are still in the business of breeding, and if they want their kids to be above average (like all the children at Lake Woebegone) , they could benefit from a new study (PDF here) by University of Notre Dame economist Kasey Buckles and graduate student Elizabeth Munnich.

In a nutshell, their research points to how to produce bright offsping.


They found that siblings spaced more than two years apart have higher reading and math scores than children born closer together.

The positive effects were seen only in older siblings, not in younger ones.

Alf learned about this from the Freakonomics blog, which says –

The authors attribute at least part of the difference to older children getting more of their parents’ time during the first formative years of their lives before a younger sibling comes along. The paper is set to be published in an upcoming issue of the Journal of Human Resources.

This has got to be good stuff for the would-be parents of the next Einstein.

Here’s the abstract:

This paper investigates the effect of the age difference between siblings (spacing) on educational achievement. We use a sample of women from the 1979 NLSY, matched to reading and math scores for their children from the NLSY79 Children and Young Adults Survey.

OLS results suggest that greater spacing is positively associated with test scores for older siblings, but not for younger siblings. However, because we are concerned that spacing may be correlated with unobservable characteristics, we also use an instrumental variables strategy that exploits variation in spacing driven by miscarriages that occur between two live births.

The IV results indicate that a one-year increase in spacing increases test scores for older siblings by about 0.17 standard deviations—an effect comparable to estimates of the effect of birth order.

Especially close spacing (less than two years) decreases scores by 0.65 SD. These results are larger than the OLS estimates, suggesting that estimates that fail to account for the endogeneity of spacing may understate its benefits.

For younger siblings, there appears to be no causal impact of spacing on test scores.

Alf isn’t strong on economic research. It’s apt to be riddled with funny formulae resplendent with Greek letters.

But the Freakonomics folks tell him the paper fills in one of the few remaining gaps in the large body of economic research that’s been done on family structure and children’s outcomes.

The researchers’ paper says we already know that children from larger families generally have lower educational attainment and IQ scores, worse employment outcomes, and are more likely to engage in risky behaviour.

It also refers to a recent literature in economics that has considered the effects of birth order.

From this we learn that later-born children have lower educational attainment, receive less parental time investment, and in some cases “have worse labour market outcomes”, which presumably means they are apt to get poor-paying employment, if any.

The study also says there is evidence – well, bugger me – that the gender composition of one’s siblings affects educational attainment, “though results are mixed”.

Birth spacing has received less attention – until now.

The authors sampled a nationally representative panel of 12,686 young American people ages 14 to 22 in 1979 and their children, and used the Peabody Individual Achievement Tests for math and reading to measure performance.

The largest effect they observed suggested that a one-year increase in spacing improves reading scores for older children by 0.17 SD — which would be three times the effect of increasing annual family income by $1,000.

It’s got to be worth applying this knowledge to your family planning programme, if you are still spawning.

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