There is an interesting - but terribly sad - case of a girl named Genie, who had no exposure to language for the first 10 years of her life. There is a documentary about her story and the attempts at her rehabilitation when she was found, including language development.
There is a lot of information written about her case that you can look up if you'd like. The documentary is called "Secret of the Wild Child", if not available to view (which I really hope you do get to watch) you can read the transcript here: http://www.pbs.org/wgbh/nova/transcripts/2112gchild.html
After reading about Genie, please tell us if her case provides an even clearer answer to the question: Which factor is most important in language acquisition?
As indicated by Dornyea (1994), the use of language, either in oral or written form, is an engagement in a cooperative effort of understanding between speakers and listeners or writers and readers. However, in a speech situation, the speaker has ways of encouraging the listener's understanding because of the ...
Discussion about one paragraph on question posed.