There are statistics on education level. For example "Share of the population aged 25-64, by educational attainment level, by place of birth and by sex, EU-28, 2016". http://ec.europa.eu/eurostat/statistics-explained/index.php/....

Now let's say that you make it difficult (either deliberately or due to language barriers) for individuals in the left-most part of that graph to stay. What happens long term? I don't know.