A new study (PDF of the study here) by University of Notre Dame economist Kasey Buckles and graduate student Elizabeth Munnich finds that siblings spaced at least two years apart have higher reading and math scores than children born closer together. The caveat is that this positive effect wasseen only in older siblings, not in younger ones.

The abstract from the paper:

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.

Now you know…

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(via Freakonomics)