The average weight for a 13-year-old girl or boy is 100 pounds, according to CDC growth charts. Statistically, girls average 101 pounds at age 13, while boys weigh 100 pounds. The normal weight range is 75 to 147 pounds for girls and 74.5 to 144 pounds for boys.
The average weight of a child means that about half of the kids of that particular age weigh more and half weigh less. From a percentile perspective, an average-weight child would be in the 50th percentile, with half of the kids that age in higher percentiles and half in lower percentiles.
Children with special needs may not follow these average growth patterns. For example, children with Down's syndrome may not weigh an average of 100 pounds at 13 years old. Pediatricians and other medical specialists are the best resources for information regarding a child's specific growth and development.
It is important to note that teens have growth spurts, so a 13-year-old may be below average in weight on his birthday, but by the end of the year, he may have caught up and surpassed the average. Teens gain and lose weight very quickly and may grow several inches in height in a short time frame, bringing them back into the average weight range.