The school playground provides a world in microcosm; a unique world, which grown-ups soon forget. At least, they mostly forget the intensity of the subjective experience which children have in the playground. We know that time in the playground is an appreciable percentage of time in school (see Chapter 1). It also can be a time of intense social interaction and marked physical activity. Playgrounds often provide generous space, and also a greater number of about-the-same-age play companions than is usually otherwise experienced. We can learn a lot about children’s development from what they typically do with these opportunities. And children can learn a lot, too. What we can learn about children, and what children are learning themselves, will be the themes of this chapter.