Physical Development

Growth during the period averages 3-3.5 kg (7 lb) and 6-7 cm (2.5 in) per year (see Figs. 9-1 and 9-2 on the Nelson Textbook of Pediatrics website at www.expertconsult.com ). Growth occurs discontinuously, in 3-6 irregularly timed spurts each year, but varies both within and among individuals. The head grows only 2-3 cm in circumference throughout the entire period, reflecting a slowing of brain growth. Myelinization is complete by 7 yr of age. Body habitus is more erect than previously, with long legs compared with the torso.

Growth of the midface and lower face occurs gradually. Loss of deciduous (baby) teeth is a more dramatic sign of maturation, beginning around 6 yr of age. Replacement with adult teeth occurs at a rate of about 4 per year, so that by age 9 yr, children will have 8 permanent incisors and 4 permanent molars. Premolars erupt by 11-12 yr of age (Chapter 299). Lymphoid tissues hypertrophy, often giving rise to impressive tonsils and adenoids.

Muscular strength, coordination, and stamina increase progressively, as does the ability to perform complex movements, such as dancing or shooting baskets. Such higher-order motor skills are the result of both maturation and training; the degree of accomplishment reflects wide variability in innate skill, interest, and opportunity.

There has been a general decline in physical fitness among school-aged children. Sedentary habits at this age are associated with increased lifetime risk of obesity and cardiovascular disease (Chapter 44). The number of overweight children and the degree of overweight are both increasing; although the proportion of overweight children of all ages has increased over the last half century, this rate has increased over four-fold among children ages 6-11 yr (Table 11-1). Only 8% of middle and junior high schools require daily physical education class. One quarter of youth do not engage in any free-time physical activity, whereas the recommendation is for 1 hr of physical activity per day.

Perceptions of body image develop early during this period; children as young as 5 and 6 yr express dissatisfaction with their body image; by ages 8 and 9 yr many of these youth report trying to diet, often using ill-advised regimens. Loss of control (binge) eating occurs among approximately 6% of children of this age.

Prior to puberty, the sensitivity of the hypothalamus and the pituitary changes, leading to increased gonadotropin synthesis. For most children, the sexual organs remain physically immature, but interest in gender differences and sexual behavior remains active in many children and increases progressively until puberty. Although this is a period when sexual drives are limited, masturbation is common, and children may be interested in differences between genders. Though still somewhat controversial, there is growing consensus that breast development and menarche are occurring at an earlier age among girls in the USA. Rates of maturation differ by geography, ethnicity, and country. These differences in maturation have implications for differing expectations of others about them based on sexual maturation.

Cognitive Development

The thinking of early elementary school-aged children differs qualitatively from that of preschool children. In place of magical, egocentric, and perception-bound cognition, school-aged children increasingly apply rules based on observable phenomena, factor in multiple dimensions and points of view, and interpret their perceptions using physical laws. Piaget documented this shift from “preoperational” to “concrete logical operations.” When 5 yr olds watch a ball of clay being rolled into a snake, they might insist that the snake has “more” because it is longer. In contrast, 7 yr olds typically reply that the ball and the snake must weigh the same because nothing has been added or taken away or because the snake is both longer and thinner. This cognitive reorganization occurs at different rates in different contexts. In the context of social interactions with siblings, young children often demonstrate an ability to understand alternate points of view long before they demonstrate that ability in their thinking about the physical world. Understanding time and space constructs occurs in the later part of this period.

The concept of “school readiness” is controversial. There is no consensus on whether there is a defined set of skills needed for success on school entry, and whether certain skills predict later achievement. By age 5 yr, most children have the ability to learn in a school setting, as long as the setting is sufficiently flexible to support children with a variety of developmental achievements. Rather than delaying school entry, high quality early education programs may be the key to ultimate school success. Separation anxiety, or school refusal, is common in the early school years.

School makes increasing cognitive demands on the child. Mastery of the elementary curriculum requires that a large number of perceptual, cognitive, and language processes work efficiently (Table 11-2