The Japanese aspectual form teiru marks 'the durative phase of a situation' (Shirai, 2000: 333) and has four distinct meanings, progressive, resultative, perfect, and habitual. Because of the complex concepts and the polysemous nature of the structure, even advanced learners' understanding and ability to interpret and produce appropriate teiru forms is at times fragmented and incomplete (e.g., Nishi, 2018; Shirai and Kurono, 1998; Shibata, 1999; Sugaya, 2002). This paper considers how Concept-Based Language Instruction (C-BLI) can help L2 beginning learners of Japanese, who were introduced to teiru for the first time, develop understanding of the target concept. C-BLI teaches categories of meaning and how they are connected to forms through the materialization and transformation of conceptual understandings (Garcia, 2018; Lantolf et al., 2020). The instruction was conducted in a collegelevel intact first-year Japanese class for six weeks. This paper presents findings that illustrate the development of the entire class, focusing on the transformation in two focal students' understanding and interpretations of the teiru form.
