Since Kenya's independence in 1963, ethnicity has been an important factor in Kenyan politics and everyday life. While recent research has shown that ethnic favouritism impacted the allocation of educational resources in the past, so far, no systematic research has been conducted on how teachers exacerbate, mitigate or countervail the political culture of ethnicity and ethnic favouritism. As agents of socialisation, teachers’ attitudes and behaviour can, consciously or unconsciously, convey the message that ethnic favouritism is normal and socially acceptable, or conversely delegitimise such practices. Based on a list experiment among 894 secondary school teachers in the county of Nairobi, we find that at least 25% of teachers have already favoured coethnic pupils. Interviews indicate that such favours are seldom blatant in nature and mainly serve to show solidarity with one's kin. Still, even small – frequently well-intentioned – favours may damage inter-group attitudes, trust and relations, and may even contribute to the persistence of ethnic politics.