Abstract This longitudinal study investigates the development and interrelation of adolescent learners’ L2 English vocabulary knowledge and extramural English (EE) input. The study examines the longitudinal development of L2 English receptive vocabulary knowledge, EE input and the dynamics between L2 proficiency and EE input. Data were collected at four time points by administering vocabulary tests and questionnaires on EE activities. Generalized additive mixed models and growth curve models indicated significant vocabulary growth, particularly in the early years of secondary school, which slowed down toward the end of the study. EE activities such as gaming, social media and reading positively predicted vocabulary development, while watching television with L1 subtitles had a negative effect. Temporal network analysis revealed reciprocal relationships, suggesting that L2 proficiency influences EE input and vice versa. The findings underscore the importance of EE in L2 vocabulary development and highlight the dynamic interplay between language learning and extramural activities.
Vanessa De Wilde (2025) studied this question.