•Some aspects of the second language develop according to ‘natural sequences of development and learners may be more likely to learn certain sequences of development and learners may be more likely to learn certain language features when they are developmentally ‘ready.’•Other aspects of language, however, for example, vocabulary, can be taught at any time, as longas the learners are interested in the opportunity to learn and the teaching methods are appropriate to the learner’s age, interests, and learning styles.•Learners can learn a great deal that no-one ever teaches them.