The process of learning a first language is commonplace in one sense and deeply mysterious in another. It's commonplace because everyone does it. A newborn infant knows almost nothing about the language being spoken around her, but around the time of her first birthday she will start saying her first words. Somewhere between the ages of one and two she will start putting two words together, and sometime after her second birthday she will produce sentences of increasing complexity, all the while learning new words at an incredible rate.

But learning a first language is mysterious because so much of it happens at such a young age.We don't remember doing it ourselves, and the children who are learning now can't tell us much about what they're doing. Researchers who study how children learn language have to come up with creative experimental techniques to explore what their young subjects know.

Learning to talk does more than help young children express what they want (and respond to instructions); speaking is an important part of becoming a full member of the community. This may explain why many people have strong beliefs about first-language acquisition – how children do it, how adults can help, and what the process means for children's eventual place in the world. In this chapter, we'll see that these beliefs are highly culture-specific, and that some beliefs about language acquisition common in western cultures are either based on uncertain evidence or simply wrong.

This chapter focuses especially on the idea that parents teach language to their children explicitly. Mainstream middle-class western parenting practices put a high value on the parent's role as a teacher, and this includes teaching language; parents are expected to train their children on words for colors, shapes, animal sounds, and so on. One question we will explore is whether the parent-as-language-teacher is a universal model of child-rearing: do all cultures include language teaching in a parent's duties? As it turns out, different societies have very different ideas about how children are supposed to learn language.

Parents’ role in child language acquisition isn't just theoretically interesting; it also has important real-world consequences. If language must be taught, then it's possible to teach it badly.