Sibling effects on Numeracy and Literacy achievement: Evidence from Two Large French Cohorts

We studied the effect of the number and characteristics of siblings (sex and age), on school achievement in numeracy and literacy from kindergarten to 5th grade, in two large French cohorts (the Elfe cohort, more than 4,400 children, and the DEPP panel, more than 9,500 children). Running linear mixed effects models, we find that, independently of socio-economic status, having more siblings is always negatively associated with school achievement. This is the case for both older and younger siblings, and for brothers and sisters. Our results are in line with the resource dilution model (i.e., in families with more children there are fewer resources available per child) and do not support the confluence model (i.e., a child’s intellectual environment is influenced by the average intellectual ability in the family), since for example, the association between the number of siblings and the achievement score is more negative for older than for younger siblings. We also find that these negative effects are partly mediated by parental interactions, once again supporting the resource-dilution hypothesis. Finally, although the association between the number of siblings and achievement scores is not moderated by the language spoken by the parents, it is moderated by the family income, with a less negative association in wealthier families.