My answer to the question: “When is the best time for a child to learn English?” on Quora.com
The best time for children to develop a native-like “feel” for English intonation is birth-minus-5 months, in other words, in their mother’s womb. During the later part of gestation, babies in the womb listen to their mother’s intonation and become accustomed to the tonal flows of the language she is speaking. So if mom can do so, she should talk and sing in English so when she’s pregnant.
The best time to acquire English is from 0–8, when children are also acquiring a first language. Research now shows that children’s brains do not get confused hearing and processing two languages,so they will be able to acquire their first language and English at the same time.
The best school years for children to receive instruction in English as a second language are ages 4–8. During that time, our children’s brains are laser-focused on acquiring and organizing a language system so they can communicate and survive, and they learn languages quickly and easily. Instruction for youngsters this age means lots of exposure, games, songs, rhymes, poems, chants, movies, as well as interaction in English with people in their family and, if possible, teacher or tutor guided lessons.
This doesn’t mean we should give up if our child is older than 8 years old. Ages 9-puberty are still very good times to learn. Children’s brains are still very pliable and designed for rapid learning, so they will make good progress learning English. Their brains have been repurposed though, from purely language acquisition, to idea acquisition, using the language they learned during their super-powered language acquisition years of 4–8.
Secondary school students must work harder to master the sounds of a new language, but they now have the intellectual capacity to understand the structure of a language and follow it’s grammar and syntax rules. So they can still make progress, but now the lessons tend toward analysis rather than synthesis.
As we grow from birth to adulthood, our brains develop different areas to focus on different skills that match our survival needs. So there are optimal times to learn different skills. Still, some people just naturally find learning a second language easier than other people. And new research shows that learning a second language at any age has great benefits to our brain’s health and well-being, even for the elderly.