Investigating spoken classroom interactions in linguistically heterogeneous learning groups – An interdisciplinary approach to process video-based data in second language acquisition classrooms

• Interdisciplinary approach to compiling a spoken learner corpus. • Publishing guidelines for processing video-based classroom data. • Reporting innovative evaluation of the robustness of annotations and transcriptions. • Presenting a L2 spoken learner corpus with rich meta-data on teachers and learners. Speaking the local language is central for successful integration into society. The teacher's language in second language (L2) classrooms serves as a crucial tool in language learning. Heterogeneity of learners’ language proficiency levels challenges teachers to adapt their language and accompanied instructional behavior. We offer an approach to study language acquisition processes and how teachers adapt their instructional language. This article presents our language-independent guidelines for processing video-based data of classroom interactions and demonstrate their reliability in a German as Second Language (GSL) classroom. These guidelines enable transcriptions of spoken language in noisy environments and detailed annotations of non-verbal classroom behavior. We outline research avenues at the intersection of empirical education research and linguistics that become feasible through these resources focusing on studying (non-)verbal adaptation strategies of teachers for learners at different proficiency levels. Our work directly fosters the interdisciplinary study of teacher-learner interactions, teacher competencies, and language acquisition.