The development of inequality during primary education: investigating the genetic and environmental sources underlying learning differences

Are differences in educational performance between pupils at the start of schooling—and their underlying genetic and environmental sources—reproduced, accumulated, or compensated over the primary school career? I investigate this using reading comprehension and mathematics test scores of over 4,000 same-sex and opposite-sex twin pairs, identified in the Netherlands Cohort Study on Education (Grades 1–5). Biometric latent growth models show, first, that most of the achievement inequality is already present at the start of education and is related to genetic variance. Second, these initial achievement differences are somewhat compensated over time, more strongly for mathematics than for reading. This leveling is related to decreasing genetic and environmental differences. Third, at the same time, new sources of achievement differences emerge during primary education that are unrelated to initial achievement. These new sources of differences are captured by variance in growth rates and are mostly genetic. As a result, although inequality linked to initial achievement decreases, the total systematic inequality in achievement increases over time because these new sources of differences outweigh the compensation of initial differences. In other words, over the course of primary education, inequality based on where children start remains prominent yet gradually decreases, while “new” inequality based on how fast children learn is simultaneously opens up.