Changes in Body Size in Middle Childhood

Parents and health care providers typically pay the closest attention to an individual child’s growth patterns. Many of us can visit the house in which we grew up and identify a marker showing that our height increased over time. Parents and health care providers are also often first to detect that children may be beginning to fall above or below the norms for their height or weight. In the majority of cases, there is no cause for alarm. Experts emphasize the need to treat these normative data as just that: an average height or weight for a given chronological age. Many children grow at different rates and follow different growth trajectories. Growth rates can vary based on genetic histories, ethnic background, illness, and other factors. For example, children from North America, northern Europe, and Africa tend to be taller than children from Asia and South America. Within the United States, African American children are on average taller than Caucasian, Asian, and Hispanic children.

Typically a pediatrician creates a growth chart for an individual child and plots his or her increases or decreases in height and weight over time. Comparisons are then made not only to the national averages but, more importantly, also to the child’s growth history. Although it may have been correct for the observer in the chapter case study to assume that the larger children were the oldest, such an observation may not prove to be true for all children.

Recognizing that growth may occur at different rates, when might there be a cause for concern? A generally accepted rule of thumb is that if a child’s height or weight falls below the 10th percentile, the cause should be investigated. When, based on national averages, 90% of same-aged children in a sample weigh more than a targeted child, or if height falls above the 90th percentile, further examination is warranted.

Height and weight data collected from children in the late 1800s has shown that children today—in almost all regions of the world—are taller and heavier. This pattern is referred to as a secular trend in growth (Tanner, 1990). Children raised in average economic conditions have increased in height approximately 2 centimeters (cm) each decade since the beginning of the 20th century. Reasons offered for this trend are multiple, complex, and include both genetic and environmental components. An evolutionary explanation for the secular change asserts that “tallness” genes are being selected over “shortness” genes (Tanner, 1978). Alternatively, environmental explanations may include improved prenatal care, immunizations, hygiene and sanitation, better nutrition, and less illness.

A related outcome to this growth trend is that girls and boys appear to be entering their second growth spurt associated with puberty earlier than ever before. Recent public health research indicates that some girls between 8 and 10 years of age are displaying early stages of pubertal maturation (Herman-Giddens et al., 1997). Earlier maturation has critical implications for social and emotional development as well as for how peers, parents, and teachers react to the maturing youth.