Many can and do.  I spoke next to ZERO English - even after spending a summer at preschool camp/toddler camp - when I entered JK, yet with hard work (and a "tutor" (basically an older kid on our street who would hang out for an hour or two in the afternoon)), I caught up VERY QUICKLY.  I was (and am still) fluent in spoken Cantonese and English, even though I can't read my ancestral language.  I not only graduated from university (majored in history and drama), but graduate school as well.  Then again, I also scored near perfect on Ms. Wente's quiz.  #willfeelguiltynow