Abstract
The present study examines the current situation and development of the vocabulary size of Japanese junior high school students learning English at the beginner level using a vocabulary size test (Sato, 2016). A total of 505 of junior high school students participated in the research and their vocabulary size was measured at the end of the first and the second term. The results show that, at the end of the first term, junior high school students have significantly different vocabulary sizes depending on their grade levels, with an average estimated vocabulary size of 795.03 for seventh-grade, 1,024.59 for eighth-grade, and 1,070.76 for ninth-grade. The acquisition process shows the different patterns for the various word frequency groups. For seventh graders, the 400 and 1,200 word groups developed significantly, while only the 1,200 word level increased significantly for eighth graders. Considering these results, further research is needed in order to state more precisely the process of vocabulary development of junior high school students as well as improvement of the test adopted in the present study.
