Investigating age in the use of L1 or english‐only instruction: Vocabulary acquisition by Korean EFL learners

This study examines the effects of teachers' language use—first language Korean (L1) or second language English (L2)—on the vocabulary acquisition and retention of two age groups: elementary school children after only a few years of English study ( n = 443) and adults at university with demonstrably higher levels of proficiency ( n = 286). Its context is the frequent recommendation by policy makers that L2 teachers should maximize the use of the target language and do so from the very beginning of instruction. We focused on the effects of language use on vocabulary learning because vocabulary teaching frequently involves L1 use even in an otherwise L2 communicative classroom. Our findings suggest that both age groups benefit from links being made with the L1, but that young learners benefit more and that differences in L2 proficiency levels, which often accompany age differences of L2 instructed learners, are a possible contributing, though not a deciding, factor in this conclusion.