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This chapter provides an overview of typical development, identifies developmental variations, and discusses several developmental disorders. This chapter does not cover typical development in the newborn period or adolescence (see Chapters 2 and 4, respectively). It addresses behavioral variations that reflect the spectrum of normal development, along with developmental and behavioral disorders and their treatment. The developmental principle, that is, the concept of ongoing change and maturation, is integral to the daily practice of pediatrics. It is the basic science of pediatrics. For example, we recognize that a 3-month-old infant is very different from a 3-year-old toddler or a 13-year-old adolescent, not only with respect to what the child can do but also in terms of the kinds of illness he or she might have. From the perspective of the general pediatrician, all these areas should be viewed in the context of a “medical home.” The medical home is defined as the setting that provides consistent, continuous, culturally competent, comprehensive, and sensitive care to children and their families. It is a setting that advocates for all children, whether they are typical or have developmental challenges or disabilities. By incorporating the principles of child development—the concept that children are constantly changing—the medical home is the optimum setting to understand and enhance typical development and to address variations, delays, and deviations as they may occur in the life trajectory of the child and the family.


Typical children follow a trajectory of increasing physical size ( and increasing complexity of function (Tables 3–1 and 3–2).

Table 3-1.Developmental charts.

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