According to a news article, some schools in Seoul have many children from immgrants family, especially from China, vitenam and Russia.
Most of them don't speak Korea well, I think that's the problem. In a globalization era, you can move anywhere to settle down howerver as the saying goes 'when in Rome, do as the Romans do', it's important for immigrants to learn the language of the country where they are in and integrate into their host community in terms of customs.
The Korean government needs to provide them with more resources to help them intergrate into Korean society.