This chapter has outlined some of the factors that we know contribute to development and that can follow an atypical trajectory. We identified two key perspectives and considered the factors within two corresponding groups: those arising from within the child (such as brain damage, genetics and the importance of critical or sensitive periods of development), and those external to the child (such as societal expectation and the self-fulfilling prophecy, labelling and the provision of appropriate opportunities and learning contexts).

This discussion of ‘within’ and ‘external’ factors deliberately raises the issue of the interplay between these two perspectives. It is increasingly recognized that the way we think about atypical development needs to take account of these two perspectives and consider the implications for how we help children who are developing atypically. At the beginning and end of this chapter, we have discussed the question of how society views developmental differences and the role that individual differences play in determining whether development is considered to be atypical. As educators, parents and policy-makers, when discussing atypical development and determining the nature of any subsequent help that is provided, we need to give consideration to the nature of societal expectations and the model of disability to which we subscribe.