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Lessons from atypical development

All parents have asked themselves why some children grow up to excel at mathematics, others to excel at languages and yet others to excel at sports. Occasionally, there are clear events that demarcate why one child has developed a strength in a particular area, but even without such obvious markers, individual children differ enormously in what they grow into. Our aim in this chapter is to introduce the notion of developmental tra-jectory (e. This is the idea that to fully understand a biological system such as the growing child, we need to consider each developmental step that the child has taken before. That is, we need to view the child as positioned on a continuous developmental trajectory rather than as simply passing through discrete stages of performance. An individual child's current position on this continuum is the outcome of a common developmental process that operates under slightly differing constraints. Children whose development follows a trajectory that is very different from the typical trajectory expected of the majority of other children offer a unique opportunity to examine how these constraints operate. Developmental disorders , then, strike at the heart of the issues we are considering in this book. What are the constraints that shape development? In this chapter, we will examine how development occurs in children with developmental disorders (see Box 11.1 What are developmental disorders?). The aim of this exercise is to explore how constraints at the genetic, neural, physical and social levels of description operate to guide cognitive development. We begin by asking what role, if any, development actually has in understanding children who follow atypical developmental trajectories. We then ask how the interactivity of brain systems constrains development, and the extent to which the timing of developmental events plays a significant role. Next, we ask what role differences in input encoding and motor abilities have on cognitive development. Finally, we ask how the child's social context can constrain development.