Differential Effects of Age, Linguistic Distance, Gender, and Education on English Proficiency: A Comparative Crosslinguistic Study of Immersion and Nonimmersion Learners

Abstract Do immersion and nonimmersion learners’ English grammaticality judgment test (GJT) scores reflect the same underlying processes in language learning? Drawing on data from Chen and Hartshorne's (2021) study, we argue that they do not. Using generalized additive mixed models (GAMMs), we found that age of onset was the strongest predictor of GJT performance among immersion learners, whereas linguistic distance was the most influential variable for nonimmersion learners. Moreover, the nonlinear effects of age of onset, length of experience, education, and linguistic distance differed substantially between the two groups. Female learners consistently outperformed male learners across both contexts. Similarly, learners residing in an English‐speaking environment scored higher on the GJT than those living in non‐English‐speaking countries.