This bold claim made by the sociolinguist Michael Halliday points to the developmental importance of language. This quotation resonated with a piece of research I was doing in an extremely disadvantaged kindergarten in the Western Cape region of South Africa. The research focused on Sipho and Nandi's verbal interaction as they were trying to build a train out of a variety of blocks. Of particular interest was how these two three-year-old children used language (in this case their mother tongue is isiXhosa, the first language of the majority of people in the Western Cape, South Africa) to solve a problem that they encountered building this train. This use of language as a problem-solving tool soon became of major interest in the research because it resonated so well with the psychological theory of learning postulated by the Soviet psychologist Lev Vygotsky (1978). Of particular interest in this context is trying to understand how humans learn together through communicative interaction. Figure 1.1 below illustrates these children as they solved their problem together.