外国に行っただけでは外国語はうまくはならない
What Does it Take to Acquire Language?

Stephen D Krashen
http://www.sdkrashen.com/articles/what_does_it_take/
Published in ESL Magazine, 2000. 3(3): 22-23.
Discussion
The case is quite consistent with current theory (e.g., Krashen, 1985; 1999), and shows that "acquisition" alone can lead to
impressive levels of competence in a second language. Armando had the necessary ingredients: comprehensible input
(although it was not comprehensible at first) and a low "affective filter." The most striking aspect of this case,
in my opinion, is the support it provides for the notion of club membership, the idea that we "talk like the people we perceive
ourselves to be." (Smith, 1988, p. 4; see also Beebe, 1985). Armando, it can be hypothesized, made the extraordinary progress
he did because he had comprehensible input and because he joined the club of speakers who used the language.
(Note that the "club" in this case was a circle of friends, not a national or ethnic group; Armando has not converted to Judaism.)
Of course, Hebrew was not comprehensible for him right away. His great accomplishment was due to patience, being willing to acquire
slowly and gradually with a long silent period (or period of reduced output). With a "natural approach" language class Armando would
have had comprehensible input right away and would moved through the beginning stages more quickly, and real conversational
Hebrew would have been comprehensible earlier.
I predict that a traditional class focusing on grammar would not have had this effect.
Armando's case also shows us that one can do quite well in second language acquisition without living in the country
in which the language is spoken and without formal instruction.
The crucial variables appear to be comprehensible input and having
a good relationship with speakers of the language.
留学しても日本人だけでつるんでいたり、コンビニに行って誰ともしゃべらなかったりじゃあ、うまくはなりませんね。