Source: The Bilingual Family: A Handbook For Parents by Edith Harding & Philip Riley, 1999, CUP.

Over half of the world’s population is bilingual. This fact is usually surprising to many Europeans, who are under the impression that living with two or more languages is exceptional. (p. 27)

What matters and what doesn’t in second language acquisition?

Singleton’s survey (1983, Age as a Factor in Second Language Acquisition. CSLC, Trinity College, Dublin) of all the reserach and evidence shows clearly that age, in itself, is not particularly relevant to success in language learning, whereas motivation and opportunity are. (p. 63)

What is the same and what is different about young and adult foreign language learners?

Children put vast amounts of TIME and EFFORT into mastering a language: where adults do likewise, they seem to learn just as well, pronunciation excepted. In fact, adults do BETTER in terms of RATE of acquisition, and not so well in terms of eventual outcome: younger people do seem to acquire native-like accents, whereas older people seldom* lose their foreign accents. (p. 63)

*Seldom* does not mean *never*! I have read about about studies of adult SL learners with native-like accents in “The Study of Second Language Acquisition” (2008, 2nd edition, OUP) by Rod Ellis.

Update 24-12-12 an interesting discussion initiated by speakers of English about ways of acquiring a native-like Chinese accent