2023 年 34 巻 p. 161-176
This study reports on whether or not knowing the results of a diagnostic test measuring the degrees of nativelikeness of word clusters in the mental lexicon (ML) boosts the effects of a self-study online vocabulary learning program (Word Cluster Master Program: WCMP) that the authors developed to promote the restructuring of the L2 English ML of Japanese EFL learners. Thirty college students in a High (CEFR B2 and C1 levels) group and a Low (CEFR A2 and B1 levels) group, respectively, took the diagnostic test and were told their results before working on the WCMP, which takes six weeks. The results showed that the cluster structures in the ML were statistically significantly different between the groups before starting learning with the WCMP, but after the six-week program, this difference was gone, indicating that the restructured ML structures of the groups turned out to be quantitatively similar to each other. High percentages of learners in the High group (67%) and in the Low group (73%) produced a perfect word cluster structure in the posttest, whereas much lower percentages of 7% and 17% did so in the treatment groups for two of our previous studies (Orita, et al., 2016, 2019), respectively. This suggests that introducing the results of the diagnostic test prior to executing the WCMP is effective. Future studies are also discussed.