| At Birth | At Maturity (25 years) |
| Stomach undeveloped | Complete digestive development |
| Few digestive juices | All |
| No provision for digesting starch until 8 or 9 months; fats (except cream); protein (except curds of milk); solid food | Digestion of all food elements, including solids |
| No teeth cut | Two sets of teeth cut |
| Sense organs: incomplete development, especially sight and hearing | Senses fully developed |
| Fine sense discrimination | |
| Reproductive system rudimentary | Reproductive system mature |
| Nerve cells undeveloped | Nervous system complex and developed |
| Few association fibers formed | |
| Medullary sheath not formed | |
| Motor ability limited to crying, grasping, reflex movements of arms and legs | Motor coördination of all muscles, including accessory eye and finger muscles |
| Mental ability limited to few vague, unlocated sensations, slight motor memory | Concentration, imagination, judgment, speech, all well developed |
| Language only a cry or instinctive movements of head, arms, legs | Fluent use of language |
| Emotions limited to slight pleasure-pain; no control | Wide range of emotions, potentially controlled and expressed |
| Volition rudimentary | Will power to achieve any purpose |
| Social, moral, religious instincts undeveloped | Sense of law and property rights |
| Social coöperation | |
| Moral standards, judgments, and habits | |
| Religious feeling and action |
After twenty-five years there is sometimes a slight increase in height and weight; plasticity is slight; new habits are not readily formed; new ideas not readily accepted. The nervous system is capable of continued development.
There are a few foundation facts and principles that should be summarized before taking up in detail the stages of growth and development.
The child is not a small edition of an adult. His anatomical proportions, his physiological processes, his ways of thought and of thinking, his motives, interests, likes, emotions, methods of expression, are all different from the adult’s; and they are all different at different stages in his development.
The child lives through (recapitulates) in a general way the main stages and order of physical and psychological development that organic life and the race have passed through in the countless ages since life began. Starting as a one-celled creature, he recapitulates in the nine months of embryonic life the processes of evolution that required millions of years, from the amœba to the higher vertebrates, in the evolution of the species.
At birth the baby is less developed and more plastic than the young of any other creature at its birth. This helplessness and plasticity are due to the incompleteness in development of the nervous system. It is because of this incompleteness that the physical, mental, and spiritual life can be shaped in great measure by environment. It is this incompleteness that provides both the opportunity and the responsibility of parents and guardians.
For normal development there must be both the growth principle and power within the individual, and the growth stimulus and materials supplied by the environment.
The rate and nature of growth and development are influenced by two factors: (1) heredity (race, family); (2) environment (climate, social status, economic resources, city or country, materialistic or idealistic atmosphere, commonplace or cultured, ugly or beautiful, expressive or repressive, guiding or neglectful).
Growth and development are two different processes. Growth is increase in size; development is increase in power of function. This principle holds true for every muscle, every nerve, every special organ, every brain center.
Growth is a vegetative process, dependent upon intake of nutrition and elimination of waste. Development is dependent upon use, which involves the exercise of the organ or system and of the related brain center, and this leads to both (a) the initial use of mind and (b) mental development.