Study shows in young bilingual children, the languages develop simultaneously but independently. Also that Spanish is vulnerable to being taken over by English, but English is not vulnerable to being taken over by Spanish. It isn't the quantity, but the quality of the language exposure that matters.

I grew up in San Diego. I took Spanish as a second language and ended up moving to Mexico for a few years once I turned 18. In my Spanish classes it always seemed the English primary language kids learned textbook Spanish better, me included. Once I moved to Mexico it was almost like my second semester in class. My experience is pretty subjective but everything I learned in class really only gave me a basis to relearn Spanish while I was immersed. I get a lot of complements for my Spanish skills but I put it in the perspective that I can speak like a middle schooler but understand as a high schooler. I can totally see the disconnect in quality of US education on English vs Spanish. I can imagine a non native English speaker being focus on English and learning it at a higher caliber. I will say based on my experience though most English as a second language students focused more on English and may have left Spanish behind just because it is what they are focusing on. This is all still pretty fascinating to look on. I'm glade I got the chance to be immersed in another language in a non schooling setting.

/r/science Thread Parent Link - eurekalert.org