Family Income Shapes School Readiness in Landmark Study of 268,000 Korean Children

Children from lower-income families in South Korea are significantly more likely to start school without the basic skills and attitudes they need to thrive, according to one of the largest studies of school readiness ever conducted. The research, published in BMC Pediatrics, followed 268,407 children born in Korea between 2008 and 2012 and found that those in the lowest income bracket faced a 17 percent higher risk of being unprepared for school in at least one key developmental domain compared with children from the highest income households. The finding, drawn from a truly population-wide dataset, adds powerful statistical weight to a question that has long concerned educators and pediatricians alike: how deeply does a family’s financial situation reach into a child’s earliest learning?

School readiness is more than a buzzword. It describes whether a six-year-old can sit still, follow instructions, express needs, play cooperatively, show initiative, and sustain attention long enough to absorb lessons. Decades of research have linked these early capacities to later academic achievement, social well-being, and even adult health outcomes. Children who arrive in the classroom already struggling often face a widening cascade of difficulties, from poor reading scores to behavioral problems, that become progressively harder to reverse. That is why researchers are increasingly treating the years before formal schooling as a critical window for intervention, and why the new Korean study matters far beyond its national borders.

The scale and design of the study set it apart. Rather than sampling a few thousand families, the investigators tapped two national data systems: the Korean National Health Insurance Service, which tracks virtually every resident, and the National Health Screening Program for Infants and Children, which collects developmental information at prescribed ages. Parents completed school readiness questionnaires when their children were between 54 and 60 months old, just before the typical school entry age. Crucially, the team excluded children born prematurely or with low birth weight, as well as those with perinatal complications, sharpening the focus on family income as a variable in otherwise relatively healthy children.

A particularly clever methodological choice strengthened the analysis. Instead of relying on self-reported earnings, which families often misstate, the researchers classified income using the amount of insurance copayments in each child’s birth year. Because Korea’s national insurance system calculates copayments directly from household income, this measure offers an objective, administratively verified proxy for family finances. The cohort was then divided into three groups: a low-income group below the 25th percentile, an intermediate group between the 25th and 75th percentiles, and a high-income group above the 75th percentile. Of the 268,407 children, 76,017, or 28.3 percent, fell into the low-income category, 146,496, or 54.6 percent, into the intermediate group, and 45,894, or 17.1 percent, into the high-income group. Slightly less than half the sample, 49.2 percent, were boys.

The primary outcome was the risk of unreadiness on at least one of six domains measured by the questionnaire: interest in school, ability to play, initiative to do things, ability to concentrate, self-control, and ability to express oneself. After adjusting for confounding factors, children in the low-income group had an adjusted odds ratio of 1.17 for unreadiness in at least one domain compared with the high-income group, with a 95 percent confidence interval of 1.12 to 1.23 and a p-value below 0.001. In plain terms, even after accounting for other influences, growing up in a lower-income household measurably raised the odds that a child would enter school missing at least one foundational skill.

When the researchers drilled down into the individual domains, the pattern held in five of the six. Children from low-income families showed elevated risks of unreadiness across nearly every dimension examined, from sustaining attention to expressing themselves and exercising self-control. This breadth is striking. It suggests that economic disadvantage does not target one narrow skill but instead exerts a diffuse pressure across the whole developmental profile, touching the social, emotional, and cognitive capacities that classrooms assume children will bring with them on day one.

One of the most intriguing findings emerged from the interaction analyses. The association between family income and school unreadiness differed according to whether a child had atopic dermatitis, the chronic inflammatory skin condition commonly known as eczema, with the statistical test for interaction yielding a p-value of 0.043. Atopic dermatitis affects a substantial share of young children and is associated with sleep disturbance, itching, and discomfort, all of which can interfere with concentration and emotional regulation. The result hints that physical health conditions and socioeconomic disadvantage may compound one another, stacking risks in ways that single-factor studies miss. It also raises the possibility that treating common childhood ailments more aggressively in disadvantaged families could partially buffer the developmental toll of poverty.

The authors are careful about what the study can and cannot show. As an observational cohort, it demonstrates association rather than proven causation, and income itself is a stand-in for a web of intertwined factors: parental education, housing quality, nutrition, stress, access to books and enrichment, and time available for interaction. Still, the sheer size of the cohort, the objective income measure, and the exclusion of medically vulnerable children make the income gradient difficult to dismiss as statistical noise. The consistency of the effect across five of six domains reinforces the conclusion that the pattern is real and consequential.

The policy implications are hard to ignore. Korea is a high-income country with universal health insurance and extensive early childhood programs, yet even within this comparatively supportive environment, an income gap in school readiness is clearly visible at the population level. The researchers argue that considerable efforts should be made at the structural level to better prepare preschoolers from lower-income families, framing the issue not as a matter of individual parenting but as a societal responsibility with downstream consequences for academic achievement, social well-being, and future health. Interventions could include expanded access to high-quality preschool, targeted developmental screening in low-income communities, and integrated support that addresses both educational and health-related barriers.

For the global audience, the study offers both a warning and a template. The warning is that socioeconomic disparities in child development emerge early, are detectable before the first day of school, and span multiple domains of functioning, meaning that waiting until children fall behind academically may already be too late. The template is methodological: by linking national insurance records with standardized developmental screening, countries with universal health systems can monitor school readiness at scale and identify where support is needed most. As the researchers conclude, the goal is to ensure that every child, regardless of the household they are born into, arrives at the classroom door equipped to learn, connect, and flourish.

Subject of Research: The association between family income and school readiness in six-year-old children in Korea

Article Title: Influence of family income on school readiness in children: a population-based study in Korea

Article References: Lee, W. S., Kwak, J. H., Kim, J. H., Lee, G. C., Han, B. E., Shin, J., Ha, E., Lee, E., Lee, S., & Han, M. Y. (2026). Influence of family income on school readiness in children: a population-based study in Korea. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07769-4

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07769-4

Keywords: school readiness, family income, child development, pediatrics, health inequality, Korea, cohort study, early childhood education, atopic dermatitis, school readiness questionnaire, population-based study, BMC Pediatrics