environment probably has its limits, but whatever those limits are, they have not been determined as yet. How much human variability is caused by genetic factors that cannot be modified by environmental differences probably never will be known, because we have not attained that Utopia in which every child is adequately loved, nourished, and stimulated. Until such a point is reached, our only way of improving the lot of the individual and of all humankind lies in identifying the environmental elements that produce the most satisfactory results and making needed changes in the environment accordingly.
Although Jensen says that he approves of such continuing research and experimentation, his conclusions unfortunately are more consistent with the idea that children's cognitive levels are predetermined at conception and that there is little point in improving their living conditions in the hope that they will develop their best potential. His findings therefore have been eagerly taken up by individuals who take a more pessimistic and fatalistic view of humanity and who feel that there is little point in wasting time and money on experimental programs like Operation Head Start, child care centers, and other attempts to improve the environment of the children of poverty.
The middle and later childhood years span the period between the end of the preschool period and adolescence. The growth curve settles down to a steady rate throughout most of this period, until the prepuberal growth spurt.
During later childhood, sensorimotor skills are refined and extended. A study by Goodenough showed that speed of response increases steadily throughout these years. Task learning is less specific among younger children, as is indicated by the observation that the correlations between the learning of different motor tasks are higher for that age group.
The hyperactive-child syndrome is believed by some specialists to be caused by a minor neurological impairment or imbalance--minimal brain dysfunction, or MBD. To support this view, they point out that hyperactive tendencies frequently appear before the child is two years old, that such children are likely to have a history of accidental poisoning or fathers who were also restless and quicktempered. Amphetamines seem to have a calming effect on many hyperactive children, just the reverse of the effect these drugs usually have on adults. Critics of drug therapy argue that such drugs are dangerous, that they teach drug dependency, and that they are often prescribed on the mere suggestion of teachers or school officials. Furthermore, there is