Non-Technical Summary:
A growing number of studies find that birth order affects educational attainment and labor market outcomes: younger siblings within the same family have consistently worse adult economic outcomes than their elder siblings.
In this paper, we investigate when these birth order differences appear and how they evolve from birth to adolescence. We document differences by order of birth in development measures and standardised tests scores from toddlerhood to adolescence using U.S. data from the Children of the NLSY79.
As early as age one, later-born children score lower than their older siblings. The birth order gap increases until school entry and remains substantial thereafter. Parental behavior matches the pattern: mothers are more likely to take risks during pregnancy and are less likely to breastfeed their younger children.
Furthermore, parents provide less cognitive stimulation for their later-born children. Variations in parental behavior can explain a large portion of the birth order differences in test scores before school entry. Contrary to popular belief, we do not find any birth order effect on temperament and other measures of soft skills, nor differences in parental emotional support by order of birth.
Taken together, our findings suggest that a plausible explanation for the negative relation between birth order and educational achievement is a broad shift in parenting, especially with respect to parents’ ability to foster early cognitive development. Significant variation in parental behavior during pregnancy and the first few years of life, as well as the absence of any differences in the quality of emotional support, are consistent with the explanation that parents are choosing to relax what they might deem as non-essential rearing needs for their later-born children.
For most parents, it is probably not difficult to understand how and why one’s parenting focus and behavior may change with his/her later-born children. Lessons from past experiences and additional constraints on time, resources, and attention necessitate adjustments in their attitudes and beliefs about what may be possible to accomplish as parents. These broad shifts in parental behavior appear to set later-born children on a lower path for cognitive development and academic achievement, with lasting impact on adult outcomes.