Monozygotic twin differences in school performance are stable and systematic

• Published in: Developmental science 2018-11, Vol.21 (6), p.e12694-n/a
• Main Authors: Stumm, Sophie, Plomin, Robert
• Format: Article
• Language: English
• Subjects: Academic Achievement; Academic Performance; Adolescent; Age; Attitude; Child; Children; difference scores; Environmental factors; Environmental Influences; Gene-Environment Interaction; Genetics; Genotypes; Humans; Individual Differences; Individuality; Intelligence; learning; Monozygotic twin; non‐shared environment; Personality; Psychological Characteristics; school performance; Scores; Student Attitudes; Twins; Twins, Monozygotic - psychology
• ISSN: 1363-755X; 1467-7687; 1467-7687
• DOI: 10.1111/desc.12694

School performance is one of the most stable and heritable psychological characteristics. Notwithstanding, monozygotic twins (MZ), who have identical genotypes, differ in school performance. These MZ differences result from non‐shared environments that do not contribute to the similarity within twin pairs. Because to date few non‐shared environmental factors have been reliably associated with MZ differences in school performance, they are thought to be idiosyncratic and due to chance, suggesting that the effect of non‐shared environments on MZ differences are age‐ and trait‐specific. In a sample of 2768 MZ twin pairs, we found first that MZ differences in school performance were moderately stable from age 12 through 16, with differences at the ages 12 and 14 accounting for 20% of the variance in MZ differences at age 16. Second, MZ differences in school performance correlated positively with MZ differences across 16 learning‐related variables, including measures of intelligence, personality and school attitudes, with the twin who scored higher on one also scoring higher on the other measures. Finally, MZ differences in the 16 learning‐related variables accounted for 22% of the variance in MZ differences in school performance at age 16. These findings suggest that, unlike for other psychological domains, non‐shared environmental factors affect school performance in systematic ways that have long‐term and generalist influence. Our findings should motivate the search for non‐shared environmental factors responsible for the stable and systematic effects on children’s differences in school performance. A video of this article can be viewed at: https://youtu.be/0bw2Fl_HGq0 The graphical illustrates that monozygotic twin (MZ) pairs’ differences in school performance are positively correlated with MZ differences in other learning‐related traits, such as cognitive ability, conscientiousness and academic self‐concept. Thus, the twin within an MZ pair, who scored higher on school performance, also scored higher on all learning‐related traits than the other twin. This finding suggests that non‐shared environmental experiences have stable and systematic effects on school performance.