Within-person variability in performance across school subjects

Although thought to be substantial, within-person variability in performance across school subjects has not been systematically studied. Here we analysed data from the Twins Early Development Study (TEDS; Nmax = 5,919) to describe within-person variability across grades in English, maths, and science from age 7 to 16 years. We found that within-person grade variability was largely unstable across subjects and ages. Within-person grade variability at age 16 was not associated with any of 15 variables that typically explain between-person differences in school performance (e.g. IQ, socioeconomic status, and personality traits). Also, within-person grade variability did not predict later educational outcomes at ages 18 and 21. Our findings suggest that within-person grade variability is observable, but did not emerge in this study as a meaningful psychological construct. We conclude that understanding the causes and consequences of within-person grade variability is of limited epistemological value.