Naoya Shibata

Theme-based instruction (TBI) is one of the models of content-based instruction, in which learners study topics that are interesting and relevant to them (Brinton & Snow, 2017; Snow & Brinton, 2023). Although this approach is well-known in many English-as-a-second/foreign-language (ES/FL) educational contexts (Brown & Lee, 2015; Curtis, 2017; Yugandhar, 2016), research on the effects of TBI on students’ writing performance is still scarce (Ostovar-Namaghi & Nakhaee, 2019). To address this research issue, the authors conducted a one-shot model of a quantitative study with 86 first-year university students in Japan over a 15-week semester. The course covered four thematic units. The authors collected students’ perceptions of each theme before learning the unit content and their pre-/post-timed writing papers about each theme. The Wilcoxon signed-rank tests were conducted to analyze their writing samples from two perspectives (the number of tokens and syntactic complexity). Regardless of assigned themes, statistical test results revealed that the number of word tokens increased significantly, whereas syntactic complexity did not. Based on these findings, TBI does not appear to be a practical approach for facilitating learners' writing abilities to use grammatically complex sentences. Hence, other teaching approaches need to be explored and integrated with TBI when syntactic complexity development is a teaching and learning objective in writing courses.