We study the effect of ethno-linguistic classroom composition in college on educational performance, educational choices and post-graduation migration in a setting of quasi-random assignment to undergraduate seminars at a British university. We focus on two core variables: the share of non-English-speaking students and the diversity within the group of non-English-speaking students with respect to their linguistic background. English-speaking students are largely unaffected by the ethno-linguistic classroom composition. Non-English-speaking students benefit from a larger diversity in their performance and increase their interaction with English-speaking students. Educational choices of non-English-speaking students become more similar to choices of English-speaking students in response to more diverse classes. Post-graduation, non-English students who have been assigned to higher shares of non-English students in the compulsory stage are more likely to leave the country. Our results imply that current levels of internationalisation do not impose a threat to native education. Avoiding segregation along ethnic lines is key in providing education for an internationalised studentship.