While most research has focussed on the experiences and consequences of ethnic discrimination for students, little is known about how teachers respond to ethnic discrimination. Teachers' responses are important as they may affect the outcomes of ethnic discrimination for students. Additionally, many studies have shown that teachers find it difficult to respond or talk about these issues but we know very little about how they act or address these challenges. Using a qualitative sample of 48 teachers, 23 students and four headteachers, this study explores (1) how secondary school teachers respond to ethnic discrimination and (2) what might explain variability in their responses. We found that teachers vary in their responses to incidents of ethnic discrimination between students (or incidents in which the teacher was a third party) in comparison with accusations of ethnic discrimination (or incidents in which the teacher was a main protagonist). When teachers responded to incidents of ethnic discrimination, they generally treat it as a learning opportunity and expect students to be 'calm', 'open-minded', 'reflective', 'respectful' and 'communicative'. However, when teachers become the centre of the debate and are accused of discriminatory behaviour, they do not apply these criteria but deny or downplay the allegations. Differences in teachers' responses were related to background characteristics (years of teaching experience, school context, ethnic background, subject of teaching), role perceptions, basic needs for teaching, perceptions of students and a fear of being perceived as a racist.