development and growth: school age and adolescence

development and growth: school age and adolescence Growth is a complex biological phenomenon and is a vital part of a child's development. The rapid growth of childhood depends on increases both in the number of cells and in the size of individual cells. Puberty is the unique stage of growth and development associated with the social and psychological changes referred to as adolescence.

The nervous and endocrine (hormone) systems are the principal mediators of growth. The hypothalamus, at the base of the brain, contains nerve cells which produce a family of regulatory hormones whose effect is to stop and start the production of further hormones from the pituitary gland. The latter, weighing only 0.5 g, has been termed the ‘conductor of the endocrine orchestra’, as its hormones exert effects on many aspects of growth, metabolism, and reproductive development.

Growth and puberty

From 4 years of age until the onset of rapid growth in puberty (the adolescent growth spurt) the average rate of growth for boys and girls is about 5–6 cm/year. During this time the ‘typical’ boy is slightly taller than the ‘typical’ girl. This situation is temporarily reversed when girls reach their adolescent growth spurt at around 11 years old, some two years earlier than boys. At age 14 years, boys are near the peak of their growth spurt and overtake girls, whose growth spurt has nearly finished. The difference in magnitude of these growth spurts largely explains the difference in final heights attained by boys compared with girls. Weight velocity is almost constant from age 3 to puberty (rising from an average of 2.0 to about 2.7 kg/year), since the increase in fat velocity balances the drop in velocity of muscular and skeletal dimensions. Body shape continues to change, since the rate of growth of some parts, such as the legs and arms, is greater than the rate of growth of others, such as the trunk. The change is a steady one, a smoothly continuous development to the final prepubescent physique, rather than any passage through a series of separate stages.

At puberty, a very considerable change in growth rate occurs. There is a swift increase in body size, a change in shape and body composition, and a rapid development of the ovaries and testes, the reproductive organs, and the characters signalling sexual maturity. Some of these changes are common to both sexes, but most are sex-specific. Some children grow slightly more slowly than others and reach puberty later than average. They do, in the end, reach a normal height, though children who have short parents tend to be short themselves. At puberty, boys have a great increase in muscle size and strength, together with a series of physiological changes making them more capable than girls of doing heavy physical work, and running faster and longer. The changes specifically adapt the male to his primitive primate role of hunting, fighting, and foraging. Such adolescent changes occur generally in primates, but are more marked in some species than in others. Man lies at about the middle of the primate range, in terms of both adolescent size increase and degree of sexual differentiation. During the adolescent growth spurt, for a year or more, the velocity of height increase approximately doubles; a boy is likely to be growing again at the rate he first experienced about age 2.

Practically all skeletal and muscular dimensions take part in the spurt, though not to an equal degree. Most of the spurt in height is due to acceleration of trunk length rather than length of legs. There is a fairly regular order in which the dimensions accelerate: leg length as a rule reaches its peak first, followed by trunk length and the body breadths, with shoulder width last amongst them. The earliest dimensions to reach their adult size are the head, hands, and feet. At adolescence, children, particularly girls, sometimes complain of having large hands and feet. They can be reassured that by the time they are fully grown their hands and feet will be a little smaller in proportion to their arms and legs, and considerably smaller in proportion to their trunk (Fig. 2).

The adolescent growth spurt in skeletal and muscular dimension is closely related to the rapid development of the reproductive system, which takes place at this time.

In boys

the first sign of puberty is usually an increase in the size of the testes and scrotum, with reddening and wrinkling of the scrotal skin. Slight growth of pubic hair may begin about the same time, but is usually a little later. The spurts in height and penile growth begin on average about a year after the first testicular acceleration. Axillary hair appears on average some two years after the beginning of pubic hair growth. In boys, facial hair begins to grow at about the same as the axillary hair appears. Breaking of the voice occurs relatively late in adolescence, and is often a gradual process and so not suitable as a criterion of puberty.

In girls

the appearance of the ‘breast buds’ is as a rule the first sign of puberty, though the appearance of pubic hair sometimes precedes it. The uterus and vagina develop simultaneously with the breasts. Menarche, the first menstrual period, is a late event in the sequence. It almost invariably occurs after the peak of the height spurt has been passed. Though it marks a definitive and probably mature stage of uterine development, it does not usually signify the attainment of full reproductive function. Early menstrual cycles may be more irregular than later ones, and often there is no ovulation. There is therefore frequently a period of adolescent sterility lasting a year to 18 months after menarche, but this cannot be relied upon in an individual case.

Nutrition

Adolescent growth proceeds at an astonishing pace — average weight increment during the adolescent growth spurt is 16 g/day for females and 19 g/day for males. It is also during adolescence and young adulthood that bones complete their maturation.

Overweight and obese conditions occurring at this age show persistent health effects decades later. Atherosclerosis (blood vessel narrowing) begins to accelerate at this age. The peak incidence of anorexia nervosa and bulimia nervosa is in adolescence. Food habits which develop as adolescents enjoy increasing independence and responsibility for their own dietary intake are believed to persist into adulthood, making this a critical time for preventive health interventions.

Dietary guidelines consist of principles based on scientific and practical knowledge about nutrient requirements, which are translated into terms that can be taught to each adolescent. Adolescents must be most aware of foods and cooking practices that result in an adequate intake of all nutrients. The basic principles of good nutrition are:

Eat a variety of foods

The best defence against nutrient deficiencies and excesses is to vary the intake among diverse groups of good foods.

Maintain a healthy weight by balancing energy intake with output.

This is the most difficult nutritional task for adolescents. Obesity is increasing at an alarming rate among adolescents. Malnutrition secondary to chronic disease is also significant world-wide. Over the past four decades, habitual physical activity has declined for adolescents and children, while energy intake has not changed, resulting in increased overweight and obesity. Restriction of intake must be accomplished carefully to assure adequate nutrient intake. Encouragement of more physical activity is critical in maintaining good body weight and composition.

Choose a diet low in fat, saturated fat, and cholesterol

This is important for prevention of chronic disease in adulthood as well as of overweight in adolescents. Arteriosclerosis is the major cause of death in adults in industrialized countries. Its antecedents are clearly in early life and must be dealt with early.

Eat plenty of fruit, vegetables and whole grains,

avoiding high-fat foods and ensuring good bowel habits.

The ‘food pyramid’ is a straightforward way of teaching good dietary practices. It classifies foods into groups and recommends the numbers of each that should served daily to achieve the principals outlined above. The guide is this:bread, cereals, and pasta: 6–11 servings
vegetables: 3–5 servings;
fruits: 2–4 servings;
dairy products: 2–3 servings;
meat, poultry, fish, and legumes: 2–3 servings;
and, at the top of the pyramid, fats, oils, and sweets, to be used sparingly.


Impaired growth is an invariable feature of children who are undernourished, whatever the cause of the malnutrition. In developed countries, the provision of inadequate amounts of food is less common but does occur, and may be the main reason for the poor growth of deprived children. Inadequate intake also occurs as a result of chronic illness, especially renal disease, infection, and psychological disturbances such as anorexia nervosa and depression. Chronic bowel disease may lead to malnutrition and poor growth.

Motor development

In its simplest terms motor development refers to movements. It includes the waddling, clumping, ungainly movement of the toddler, the fine skills of the dancer, and the enormously intricate, delicate touch of the watchmaker.

An example of fine motor skills, extending to an older age range, is that of handwriting. Up to 5 years, copying is frequent. At 5–6 years, children learn to write their own name with large writing and some reversals. At 6–7 years, the alphabet can be printed on request but there is still some reversing. From 7–8 years most children can now write and most attempt to make their letters smaller. There is some evidence of consciousness of design. At 8–9 years, some, but not all, letters are joined. This can lead to untidiness and an apparent deterioration in ability, made worse if the child is also mastering skills of punctuation and spelling. By 9–11 years, writing is now well established, with each child's individuality beginning to show. It is essential that teachers allow for individuality; for example, if a child writes naturally without joining letters this should be accepted. From 11 years upwards individual styles flourish and should be encouraged.

Understanding, learning, and behaviour

Early human understanding involves elementary forms of speech, development of the use of symbols, and consideration mostly of one's self. Thinking is limited by the difficulty the child has in taking into account more than one feature of an object at a time. Thus a red chair cannot at the same time be thought of as wooden as well as red.

Once children start school, number concepts develop quickly. At the same time comes the ability to use number-related words: ‘more’, ‘less’, ‘four’, ‘several’, and so on. Time concepts are developed more or less uniformly, at least in Western cultures. At first comes the ability to locate one event in terms of another; breakfast comes before dinner. Other concepts follow; the child's own age (approximate age 3 years) morning or afternoon (4), the day of the week (5), the approximate time (7), the month (7), the year (8), the day of the month (8). Telling the time also follows a fairly consistent pattern; at first children tell time by the hour, then by the half hour, and then quarters, and they usually develop reasonable accuracy by the age of six or seven.

From 7 to about 12 years, children learn about size, weight, and number. They begin to think logically about things they have experienced. They realize that the number of objects in a set remains constant even if the pattern is changed. They can also think backwards and forwards in time. In mathematics, this is the same as realizing that if 2 plus 2 equals 4, then 4 minus 2 must equal 2. Underlying this development is an increase in ‘flexible’ thought, being able to see things from someone else's point of view.

From about 12 years to adulthood the main characteristic is the ability to formulate general laws and principles. The thinking of this period is, in essence, the sophisticated, flexible, symbolic thought of the adult. Children become able to reason in an abstract way about matters that they have never themselves experienced. But not everyone reaches this stage, even in adulthood.

Socially, for the first two or three years the family remains the paramount influence, but from then on there is competition from peer groups and from significant adults outside the family. The first day at school is a major event in childhood and the child's first teacher is a key figure in subsequent development. From 6 years to adolescence, the more or less formal group, created by children themselves and sometimes referred to as a gang, becomes increasingly important. It offers a relief from adult supervision and meets needs not adequately catered for in an adult-orientated society. Its function has much in common with the formal groups like Brownies or Scouts but is not identical. Gangs vary in size and activity. Some devote themselves almost entirely to antisocial behaviour; others are entirely benign. What they all do is offer members opportunities to measure themselves against others, to learn co-operation between peers, and to develop a sense of ‘belonging’. This progress in socialization may be seen as a gradual transition from dependence, via interdependence, to independence.

Adolescence is recognized as a period of risk-taking behaviour, including experimentation with smoking, alcohol, drug-taking, and sexual activity. One form of risk-taking activity may lead to another, for example the association of alcohol and substance abuse with sexual initiation. At this stage, behaviour may be in turn impulsive, exploratory, excitable, disorderly, and distractible.

Donald C. Brown, and Christopher Kelnar

See also puberty.