Pre-print, Working paper: This paper analyzes in a two-country model the impact of students' mobility on the country-specific level of higher educational quality. Individuals decide whether and where to study based on their individual ability and the implemented quality of education. We show that the mobility of students affects educational quality in countries and welfare in a very different way depending on the degree of return migration. With a low return probability, countries choose suboptimally differentiated levels of educational quality, or even no differentiation at all.