=Relation of Memory to Age and Sex.= It is a common notion that memory is best when we are young, but such is not the case. Numerous experiments have shown that all aspects of memory improve with age. Some aspects of memory improve more than others, and they improve at different times and rates; but all aspects do improve. From the beginning of school age to about fourteen years of age the improvement of most aspects of memory is rapid. If we pronounce a number of digits to a child of six, it can reproduce but few of them, a child of eight or ten can reproduce more, a child of twelve can reproduce still more, and an adult still more. If we read a sentence to children of different ages, we find that the older children can reproduce a longer sentence. If we read a short story to children of different ages, and then require them to reproduce the story in their own words, the older children reproduce more of the story than do the young children.[5] [5] See age and sex graphs, pp. 184, 188, 189. Girls excel boys in practically all the aspects of memory. In rote memory, that is, memory for lists of unrelated words, there is not much difference; but the girls are somewhat better. However, in the ability to remember the ideas of a story, girls excel boys at every age. This superiority of girls over boys is not merely a matter of memory. A girl is superior to a boy of the same age in nearly every way. This is merely a fact of development. A girl develops faster than a boy, she reaches maturity more quickly, in mind as well as in body. Although a girl is lighter than a boy at birth, on the average she gains in weight faster and is heavier at twelve than a boy of the same age. She also gains faster in height, and for a few years in early adolescence is taller than a boy of the same age. Of course, boys catch up and finally become much taller and heavier than girls. Similarly, a girl's mind develops faster than the mind of a boy, as shown in memory and other mental functions. =The Improvement of Memory by Practice.= All aspects of memory can be improved by practice, some aspects much, other aspects little. The memory span for digits, or letters, or words, or for objects cannot be much improved, but memory for ideas that are related, as the ideas of a story, can be considerably improved. In extensive experiments conducted in the author's laboratory, it was found that a person who at first required an hour to memorize the ideas in a certain amount of material, could, after a few months' practice, memorize the same amount in fifteen minutes. And in the latter case the ideas would be better remembered than they were at the beginning of the experiment. Not only could a given number of ideas be learned in less time, but they would be better retained when learned in the shorter time. If a person comes to us for advice as to how to improve his memory, what should we tell him? In order to answer the question, we must consider the factors of a good memory.