Age 15 can defy the averages when it comes to the maturation and growth of boys and girls. According to the American Academy of Pediatrics' HealthyChildren website, boys and girls are well into puberty at this age and growth is one of the major changes. Girls and boys will grow in height and weight. Boys' shoulders will broaden; girls will experience the same change to their hips. Both are natural and normal, but there is no typical schedule for when these changes occur. Two children can experience the same changes at different rates and this could be considered normal for both.
How Doctors Determine What Is Normal
The Centers for Disease Control and Prevention publishes its Growth Charts for the United States. This guide includes graphs to measure height, weight and body mass for children through age 20. Pediatricians will track growth changes on these charts to determine whether the child is growing at a healthy rate or failing to thrive. Growing at a lower-than-average rate can indicate nutritional deficiencies, biological abnormality or inherited traits. To create the charts, the CDC extrapolated data from multiple sources, including national surveys and birth certificate data.
The CDC's weight-for-age graph lists the average weight of a 15-year-old boy at 126 pounds. The chart shows that children weighing 172 pounds score in the 95th percentile, or weigh more than 95 percent of boys their age. On the bottom end, boys weighing only 90 pounds fall in the 3rd percentile. For girls, the average weight is 114 pounds. Girls at 86 pounds fall to the low end of the measurement scale, in the 3rd percentile. The 95th percentile of girls at age 15 is 168 pounds, meaning that they weigh more than 95 percent of girls nationwide.
The stature-for-age percentiles track the normal height for boys and girls. The average boy's height is 67 inches, or 5 feet 7 inches tall. Boys at 72 1/2 inches tall, or 6 feet and a 1/2-inch, are taller than 97 percent of all other boys in America, while those at 61 inches fall into the 3rd percentile. For girls, 64 inches, or 5 feet 4 inches tall, is considered a normal height. To fall within the 97th percentile, a 15-year-old girl needs to only be 69 inches tall. A 59-inch tall --- or 4 feet 11 inches --- girl is in the 3rd percentile for height.
Normal Body Mass Index
Body mass index measures the proportion of height to weight. According to the CDC, a BMI between the 5th and 84th percentiles is considered healthy for children and teens. A child at the 85th percentile is considered overweight. Once crossing the 95th percentile, the child is labeled as obese. Based on this scale, a healthy 15-year-old boy as a BMI between 16.5 and 23.3. A BMI of 23.4 is at the 85th percentile, while an index of 26.8 would place the child in the obese category. Girls have a wider range of healthy weights, spanning 16.2 to 23.5. At 23.6, girls are considered overweight, while those above 28.1 are obese.