The stability of language aptitude: Insights from a longitudinal study on young learners' language analytic abilities

An enduring question in aptitude research is the extent to which aptitude is a stable trait or a time-varying attribute. If aptitude were a perfectly stable trait, interindividual differences in aptitude at one point in time should be perfectly correlated with interindividual differences at a later point in time. However, raw test scores are affected by measurement error, a result of which is that correlations between raw test scores at different points in time underestimate the correlations between the actual skills measured by these tests at different points in time. The analyses of the longitudinal LAPS~II aptitude data ($n=636$; translated and adapted versions of MLAT and PLAB subtests) take into account measurement error and indicate that the children's ability to solve the MLAT and PLAB tests at the first data collection (autumn 2017, mean age: 10;5 years) and their ability at the third data collection (spring 2019, mean age: 12;1 years) are correlated at $\rho = 0.74$ (95\% CrI: [0.69, 0.79]). This suggests that the ability to solve the two aptitude tests is not a perfectly stable interindividual trait, but that, by and large, interindividual differences are nonetheless maintained over the course of one-and-a-half years of cognitive development.