Background Studies based on teachers’ self-reports often find that teachers use different disciplinary practices towards students from minoritized ethnic-racial groups and of low socioeconomic status (SES) than towards their peers. However, these studies do not investigate actual student and teacher behaviour or underlying mechanisms. It is also unclear whether the results stemming mostly from US-based studies can be transferred to contexts outside the US. Aims The present study addresses these issues and investigates teachers’ disciplinary behaviour using videographies of real-life classrooms in Germany. This enables us to observe actual student and teacher behaviour simultaneously and investigate potential teacher-based discrimination towards students of an ethnically minoritized group and of low SES. We also examine teachers’ stereotypes as potential moderators. Sample The study is based on secondary data and includes a sample containing information on 18 teachers and around 200 students. The exact sample sizes will be available only after the analyses. Methods Student and teacher behaviour was coded in 34 10-min video sequences from 18 German and mathematics classes by trained raters blind to the research questions. The resulting data will be analysed together with demographic and questionnaire data available in the dataset using a series of multilevel logistic regressions. Results As this study is submitted as a stage I registered report, currently no results can be reported. Conclusions Results of this study will provide valuable information on classroom processes in which teacher-based discrimination might be observable. It will also elucidate the role of teachers’ stereotypes as a potential mechanism.