How long does it take to become fluent in English?

Many, many students have asked their teachers how long it will take to master English. Many, many teachers have answered, "It depends on several factors...". A new BBC Channel 4 documentary - Why Don't You Speak English? - explores this topic, looking at four immigrants who have struggled with English since arriving in the UK a year ago. "Age is the most important factor in language acquisition, says Mila Vulchanova, professor of linguistics at the Norwegian University of Science and Technology. "There is a sensitive period in language learning, which is biologically determined, with an onset at birth and a decline around puberty. So the younger the immigrant, the better. Since this decline is only gradual, teenagers are at an advantage over adults." Would you like more details? Read the rest of the article at http://www.bbc.co.uk/news/magazine-23407265">http://www.bbc.co.uk/news/magazine-23407265 .