As an English teacher, I have seen the some evidence of that old saying that if you were taken to China at one month old, you’d grow up speaking Chinese fluently. Noam Chomsky put forward the idea that we generally have a ‘black box’ inside, which is available to learn any language we are exposed to, particularly as an infant (infant means ‘non-speaker’).
I have seen many Asian pupils become excellent English speakers, and, importantly, writers and readers, able to comment at length on poems and books, and their own thought processes. Meanwhile, I have also seen many English pupils who are severely limited in these skills, as well as many who are also excellent. It seems to me therefore that – other things being equal – the home environment, and the aspirations of the parents, still must be the greatest deciding factor in their children’s success with language, and subsequent school performance.