Association for Public Policy Analysis & Management

Children born to less educated parents have significantly lower cognitive abilities and academic achievement relative to their peers born to highly educated parents (Duncan & Magnuson, 2013). Research shows that these socioeconomic gaps emerge before children enter school and grow over time (Feinstein, 2003; Bradbury et al., 2015). However, most of the research on socioeconomic gaps in cognitive abilities is based on group mean differences. While these types of analyses can shed light on inequalities on average, they cannot tell us about when or how these gaps emerge during the course of development, leaving an important gap in the existing literature. Analyses that examine individual developmental trajectories are necessary to examine how the observed gaps come to be and can inform the timing of assessments and interventions to address achievement gaps.

To my knowledge, only one study has examined inequalities in children’s individual developmental trajectories. This study found that, between Kindergarten and 3^rdgrade, low-SES children’s reading skills develop faster than those of high-SES children, after which point they develop at a slower rate (Kieffer, 2011). The current study builds on this prior work by examining the differences in the cognitive developmental trajectories of low- and high-SES children from age 5 to age 14 using data with narrower measurement intervals, allowing for a more fine-grained analysis. Because disrupted development in one domain could lead to cascading disruption in another domain (Paterson et al., 2015), I also examine both reading and math skills.

This study uses data from the Maternal and Child Supplement of the Children of the National Longitudinal Survey of Youth 1979 (NLSY), a nationally representative sample of 12,686 young men and women first surveyed in 1979. Since 1986, the biological children of the NLSY women have been followed in two-year intervals (N=11,521). I operationalize family SES using mother’s education level when children were born; high-SES children have mothers’ with a bachelor’s degree or more (13.5% of sample) and low-SES children have mothers with a high school diploma or less (22.2%). Reading recognition and math skills were assessed using the Peabody Individual Achievement Test (PIAT). I use a multi-level polynomial growth curve analyses to document developmental trajectories.

Results show that, for both low-SES and high-SES children, the developmental trajectories of math and reading skills are non-linear with a decreasing rate of growth as children grow older. However, consistent with prior literature, low-SES children have significantly lower math and reading test scores at age 5 and an overall slower rate of growth than high-SES children. This slower rate of growth leads low-SES children to fall increasingly further behind their high-SES peers over time. Yet, low-SES children experience a period of rapid growth in math skills shortly after entering school, which high-SES children do not experience. Future analyses will explore possible reasons for the difference between math and reading trajectories and will replicate the trajectories analyses using data from the UK (Millennium Cohort Study) and from Germany (National Education Panel Study) to investigate whether these inequalities in developmental trajectories are context-specific.