Sadly South Korea is diluting its gene pool and this is being reflected in the coming generation's academic attainment.

Evo and Proud:

I've published a paper on the Damunwha children of South Korea. In that country, foreign brides, mainly from Southeast Asia, produce almost 6% of births. These children do poorly at school, ostensibly because of discrimination and imperfect learning of spoken Korean from their mothers. Yet they actually do well in subjects that emphasize social interaction and spoken language. Their learning deficit is in subjects that require abstraction and memorization, such as mathematics. [Cont...]

In 2011 it was predicted that by 2020 one third of all children born in Korea would be the result of international unions.

South Korea's Multi-Ethnic Future (The Diplomat)

Currently [2011], a third of all marriages occurring in South Korea’s rural areas involve migrant wives—mostly from China and Southeast Asia—who have been matched with South Korean men. An increasing gender imbalance tilting toward males ensures this phenomenon will continue, with jarring implications for the myth of Korean ethnic homogeneity.

In June, the government announced that the number of children with at least one parent of non-Korean heritage reached 150,000 this year, a number that has increased fourfold over the last four years. They are expected to number over 1.6 million by 2020, with a third of all children born that year the offspring of international unions. [Cont...]

No idea what the actual figure is now but Korean nationalists are facing the same problems we are.