According to a new study coming out of the University of Notre Dame, spacing out the birth of children is positively associated with test scores in the older sibling. The younger sibling seemed to be unaffected by the spacing of birth, however.
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.
The paper will be published in an upcoming Journal of Human Resources.