A study led by Dr. Elizabeth Dhuey, Associate Professor of Economics at UTSC, shows that older children perform better throughout elementary school and toward post-secondary school than their younger classmates.
The goal of this study, conducted among American students, was to learn how age influences the accumulation of human capital — the skills, knowledge, and experience that an individual has — of students throughout their lives. The findings demonstrate that older students undergo greater cognitive development overall and perform better in school, allowing them better opportunities later on in their lives.
The results of the study show that “early differences in maturity can propagate through the human capital accumulation process into later life and may have important implications for adult outcomes and productivity.”
Due to better academic performance, older students have a greater chance of entering into post-secondary education. The effect is consistent across American schools with varying levels of education quality. Older students are also less likely to be incarcerated for juvenile crimes than younger students in the same grade.
In the US, a child’s entry into primary school is often dictated by a specific cutoff birth date. As a result, the children born in September will be almost a year older than their peers born in August. The existence of this age gap has increasingly encouraged parents to adopt the practice of ‘redshirting,’ whereby a child’s entry into school is delayed by a grade level in the hopes of giving them an advantage over their peers.
This study was the first to compare siblings born in August versus September, which allowed the researchers to control for the unobserved differences in student success found in separate families. Dhuey hypothesized that the variation in maturity between younger and older students may impact their human capital accumulation, with the younger, less mature children having greater difficulties during their years of cognitive development.
To test for this, a regression discontinuity framework was used. “The assumption of this kind of framework is that these children are similar except for the month they were born. We were able to even refine this more by looking at siblings [where] one was born in August and one…was born in September to make sure there were no unobserved family effects that might have contaminated our estimates,” said Dhuey.
“We also are able to control for conditions and treatments surrounding pregnancy and birth. We ultimately find that these extra controls do not alter our results, indicating that omitted-variables bias in the extant literature is likely not as large as some might fear,” the authors explained in the paper.
One of the implications of this study — which has yet to be peer-reviewed — is that schools should decrease the age gap between students in the same grades or classes. By doing so, younger and older children may receive adequate attention to supplement their learning, and the gaps in cognitive development and academic performance between them may decrease.
“I would like to try to empirically figure out what is making these age [effects] last into adulthood when the small differences in age should matter a lot less,” said Dhuey.
