Milestones Of Development

Selected cognitive milestones are presented in Table 2. It is not until around seven or eight months that infants will search for an object hidden as they watch, believing, apparently, that the object continues to exist even though they no longer see it. First words are usually uttered late during the first year, and children's first two-word sentences are typically spoken between eighteen and twenty-four months of age. Language abilities develop rapidly during the third year of life, so that by age three and a half, most children are linguistic geniuses, being able to speak their native tongue proficiently (and far better than most adult second-language learners). Children have a difficult time taking the psychological perspective of others until about three and a half to four years of age. Until this time, they often believe that if they know something (for example, that a cookie has been moved from a box to a jar), other people should know it as well, even though others have different knowledge (not knowing the cookie was moved). Understanding that people's behavior is governed by beliefs and desires, which may be different from one's own, has been termed "theory of mind" and is the basis of all sophisticated human social interaction. Thinking becomes more logical during the school years, and this is perhaps best reflected by conservation tasks, developed by the Swiss psychologist Jean Piaget. Beginning 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 already know.