The Effectiveness of Theme-Based Instruction on Japanese University Students’ Lexical Diversity in Writing

要旨

Theme-based instruction (TBI) has been prevalent as one type of effective language teaching pedagogy in various English as a-second/foreign-language-teaching contexts, including Japan. Although some research studies on the effectiveness of TBI on second language learners’ language learning have been conducted, the effects of instruction on second language writers’ writing abilities, including lexical diversity (LD), have not been fully revealed. Therefore, this research paper aims to explore the effectiveness of TBI on 45 Japanese university students’ LD in writing based on their LD scores in their essays and drafts that were analysed with text inspector (2019), Friedman tests with Bayes factors and Conover post hoc comparisons followed by the Bonferroni correction. In addition, the participants’ learning reflection notes coded thematically are considered to further investigate the effectiveness of TBI. Findings indicated that, regardless of the assigned themes, the participants developed their LD statistically significantly. Furthermore, students’ reflection notes also illustrated that topic familiarity and sociocultural scaffolding provided by the teacher-researcher, their classmates, and materials played an important role in their LD development in writing. At the end of the research paper, limitations to address will be considered for future research. テーマ型内容中心教授法(TBI)は、日本を含めた多くの第二言語もしくは外国語としての英語教育環境において効果的な言語教授法の一つとして普及している。言語学習者の言語学習におけるこの教授法の効果は研究されているが、書き言葉における語彙の多様性を含めた、ライティング能力においての効果は完全には明らかにされていない。本論文では、text inspector (2019)とベイズ推定量を用いたフリードマン検定とボンフェローニ補正されたコノバー検定で分析した学習者のエッセイ及び下書きを基に、日本人大学生45名のライティングでの語彙の多様性におけるTBIの効果を探究していく。加えて、コード化された学生たちの学習振り返りノートを用いてTBIの効果を考察していく。結果として、テーマに関係なく語彙の多様性が統計的に向上し、テーマへの馴染み度や教員、クラスメート、そして教材等によって与えられる足場作り（scaffolding）が重要な役割を担っている事が明らかとなった。最後に、将来的な研究調査のために本研究での限界点を考察する。

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