It's easier for us foreigners to become fluent in English, as (depending on the career choice) we're immersed in it whether we want it or not:
Not a day goes by where I don't post something in English, watch a video or otherwise hear some English, and occasionally make a phone call - in English, all the time using English terminology, googling in English and going home to read a book.. in English.
Upper class kids (like I was) in South America are often taught in English as well (in my case at
http://en.wikipedia.org/wiki/Congregation_of_Christian_Brothers )
In my case part of my family emigrated to Canada, and some of my sisters speak ONLY English, but even if they hadn't, I would believe myself to be fluent, and to read and write better than most native speakers.
And I would believe this of my English-taught classmates as well.