1. Sex. Girls mature at from 12 to 16 years, two years earlier than boys,—from 14 to 18 years. The period of adjustment is longer, slower, and with less stress and upheaval with boys than with girls.
2. Growth. Children above the average in height and weight at 12 years mature earlier than those at or below average height and weight.
3. Climate. Maturity is earlier in warm climates, and later in cold climates.
4. Urban or rural environment. Maturity is earlier with city children, later with country children.
5. Stimulation. Stimulating physical or psychical influences, as a stimulating diet, use of alcohol, early social dissipation, reading and plays that stimulate sex interest, tend to cause earlier maturity.
Children mentally defective, retarded, or laggards in school, are usually shorter and lighter weight and smaller lung capacity than the median for normal children.
Children above the median in height, weight, and lung capacity (the three are usually found together) are usually above the average in school grades of other children the same chronological age. Such children may be from 1 to 5 years older physiologically and mentally than children of the same chronological age who are below the median in height and weight.
Proportions.
During the entire growth period the proportions of different parts are constantly changing because of their uneven rate of growth. The awkwardness, easy fatigue, and weakness during childhood and adolescence are in no small measure due to these changing proportions and their inadequacy as compared with their adjustment in maturity.
The following variations from the average are indices of weakness, and measures should be taken for bringing them to normal.[50]