The effects of individual differences on adolescent L1 Chinese EFL learners’ incidental vocabulary acquisition through extensive reading

Abstract Research on incidental vocabulary acquisition through extensive reading has focused largely on textual features, with limited attention to individual differences, particularly in exam-oriented secondary school contexts. This study investigated the effects of individual differences on incidental vocabulary acquisition among Chinese EFL secondary school learners. Using a quasi-experimental design, pretests, immediate posttests, and delayed posttests measured five aspects of word knowledge: form recognition, meaning recognition, meaning recall, collocation recognition, and collocation recall. Over 6 weeks, the experimental group ( n = 99) read graded readers, while the control group ( n = 95) followed regular instruction. Participants’ L2 vocabulary size, L2 reading ability, and use of incidental vocabulary learning strategies were assessed through standardized tests and questionnaires. Findings indicated L2 reading ability as the strongest predictor of delayed posttest scores, while vocabulary size and strategy use correlated with, but did not directly predict, outcomes. Results underscore the need for strategic reading instruction to enhance extensive reading’s impact.