How important is pronunciation instruction for English learners?

One of the most notable identifiers of someone whose primary language is not English is speaking with an accent. While accents vary in English in different countries — and even by region within those countries — for most native speakers it is easy to tell if someone learned English later in life.

Interestingly, there are many people who spoke a language other than English as a child, learned English and now have native pronunciation in English. This generally occurs when people learn English (or another language) early in their life or during childhood.