SOURCE: David F. Bjorklund and Jesse M. Bering.
becomes more logical during the school years, and
this is perhaps best reflected by conservation tasks,
developed by the Swiss psychologist Jean Piaget. Be-
ginning around six years of age, children realize, for
example, that the amount of water one has is the same
regardless of whether the container that holds it is
short and fat or tall and skinny. Much before this
time, the appearance of ‘‘more’’ in the tall container
determines children’s thinking in such situations.
With adolescence comes abstract thought, again as
first described by Piaget. Children are able to think
scientifically and are able to reflect upon what they al-
ready know.Social/Emotional Milestones
Table 3 presents some social/emotional mile-
stones. The social smile, observed early in infancy, re-
flects a general responsiveness to people, critical for
an intensely social species such as Homo sapiens. In-
fants’ attachment to their parents is sometimes re-
flected by a wariness of strangers and by distress when274 MILESTONES OF DEVELOPMENT