Of course, the ideal way to become bilingual is to be raised in a situation where there are multiple primary languages. I was raised in such an environment -- my father is American, while my mother is Turkish. As an infant, I grew up in a house where both languages are spoken regularly. My parents have some amusing stories about the stage in my linguistic development during which I had a usable vocabulary in both languages but hadn't sorted the words into two separate sets... Such a situation is nearly impossible to reproduce in a school environment, but is interesting to think about.

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