Developmental Timetables

New parents worldwide are delighted on a daily basis by their young infant’s accomplishments. From the parents’ perspective, one day their infant is unable to crawl, does not reach for nearby objects, does not necessarily smile at them or produce words, and then the next day these abilities appear as if from nowhere. Such developmental milestones—the emergence of a key skill or ability—are viewed as important by parents, educators, and psychologists because infants reach them universally around the same age, and they are considered evidence of healthy, typical development. Moreover, because these abilities emerge in a consistent order or developmental timetable that begins at conception and continues into late adulthood—with infants, for example, able to crawl before they can walk and babble before they can talk—they are thought to be indicative about the nature of the underlying developmental processes that are involved.

Although the emergence of these skills is perhaps most apparent in infancy—during the most rapid period of development—they continue to develop through the life span, with children universally able to reason using logic by the early school years, reaching puberty and developing abstract thought at the onset of the teenage years, and then later in life experiencing a decline in mental faculties, physical strength, reaction time, hearing, and stamina. This entry covers (a) various milestones that occur on a developmental timetable, (b) when divergence from these developmental milestones should warrant concern, (c) what these milestones mean in terms of development, (d) how children transition from one milestone to the next, and (e) the concept of developmental cascades to describe [Page 605]developmental effects overtime and how one ability can induce changes in other abilities.

Developmental timetables and developmental milestones—the latter defined by the Centers for Disease Control and Prevention as “things most children can do by a certain age”—are, therefore, important pointers to where the infant, child, or adult is in the developmental process. The list of such milestones, and the timetable for when individuals reach them, is almost endless. In the first months and years of life, children have well-demonstrated timelines to develop gross motor skills (e.g., crawling and walking), fine motor skills (e.g., object grasping, stacking blocks), language skills (e.g., producing and comprehending words), thinking or cognitive skills (e.g., problem solving, categorization), and social skills (e.g., interacting in a positive way with family and friends), among other things. And later in developmental time at the origin of adulthood, individuals become more intimate in their friendships, become more sexually active, are more likely to develop mental health issues, and have an ever increasingly complex moral understanding of the world.