Abstract
As vocabulary plays an important part in L2 learning at the beginner level, investigation into vocabulary learning constitutes an essential part of second language acquisition research (Koda, 1989, Laufer, 1992, Meara, 1992). Assuming the case of Japanese, English education can provide a meaningful example. In addition, noting that precise measurements of the English vocabulary size of Japanese junior high school students have not been attained (Katagiri, 2000), the present study examines the growth of vocabulary size of Japanese junior high school students across their 3 years of English learning. For this purpose, a vocabulary size test (VST) was specially developed with a word list compiled from Japanese junior high school English textbooks based on the frequency and range of their vocabulary items (Sato, 2016). A total of 159 junior high school students participated in the research. The vocabulary size of the participants was measured five times over the period of 3 academic years at intervals of 6 months. Analysis of their vocabulary growth by frequency revealed a distinctive pattern for each level, yielding implications for more effective vocabulary teaching for learners at the beginner level in light of the characteristics of their vocabulary growth.

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