Abstract This article aims to build on prior research on translanguaging to document how linguistically and culturally diverse students in a primary ESL classroom mobilise a wide range of multilingual and multimodal resources to demonstrate their conceptual understanding of second language (L2) vocabulary knowledge during classroom interactions. The classroom interactional data will be analysed using Multimodal Conversation Analysis. The analyses of the classroom interactional data will be triangulated with the teacher’s video-stimulated-recall-interview data, which is analysed using Interpretative Phenomenological Analysis in order to analyse the teacher’s reflections on students’ use of translanguaging to externalise their thought processes. The findings demonstrate that students’ use of translanguaging resources allows for an externalisation of thinking processes which offers visible output for inspection by the teacher. The findings challenge the conventional perspective of L2 acquisition, which commonly involves comparing the learning outcomes of experimental and control groups to evaluate their L2 progress and development. I argue that students’ translanguaging practices can be used as interactional resources for them to visualise their conceptual understanding in progress, which offers valuable diagnostic information for the teacher to assess students’ current knowledge states in the learning process. The findings of this study can provide a comprehensive picture of the process of L2 vocabulary learning as an embodied activity, indicating the need for researchers to conduct fine-grained analysis of students’ translanguaging practices when documenting evidence of students’ L2 learning.