The aim of this quasi-experimental study is to investigate the effect of extensive reading (ER) on Japanese L1 learners’ receptive knowledge of high frequency English vocabulary. This study adds to existing research into the impact of ER on lexical acquisition by comparing two groups who did ER for different lengths of time, and utilising a validated testing tool as part of the assessment. The vocabulary knowledge of participants (N = 78) was pre- and post-tested using the Vocabulary Levels Test. Group 1 did ER for ten weeks and studied abroad for six weeks; Group 2 did ER for 30 weeks and did not study abroad. A Mann-Whitney test found no statistically significant difference between the groups in terms of vocabulary gains. A small effect was found for the number of words read and vocabulary gains for Group 2. These results suggest there is no difference in high frequency vocabulary gains between the students who did extensive reading over a longer period, and those who did ER for a shorter period and studied abroad. Another important finding was that the learning gains were small in comparison to other published ER studies. Possible explanations for the small gains, and limitations, are discussed.
Klassen et al. (2019) studied this question.