Typically, a child's bone age is close to his/her chronological age. For example, if a child is 8 years old, his/her bone age will be very close to 8 years. See bone age x-ray below for more details.

X-ray of the left hand and wrist to figure out how old the bones think the body is (technically called skeletal maturity). The bones grow from the end of the bones in an area called growth plates. They are completely open at birth and slowly grow to a closed position at the end of puberty. The more closed they are, the older the child’s body thinks it is. The x-ray is compared with standards for boys and girls of different ages.

Amount of bone tissue in a sample of bone.

Secreting internally; the secretion of an endocrine gland; a hormone.

Organs that secrete hormones directly into the blood stream. This is different from duct glands, like saliva glands, that secrete via ducts.

The final height attained at the end of puberty. Height is determined by bone growth. Final Adult Height is achieved when a child’s bone growth plates have fused. In females, the hormone estrogen causes fusion of the growth plates, so growth stops when estrogen reaches adult levels, about 2–3 years after the first menstrual period. For males, the hormone androgen, at first stimulates bone growth but eventually also causes fusion of the growth plates.

Growth increase for a set period of time.

A number based on dividing something into 100 parts, a group of children of the same age. The centile number tells what percentage of children that same age are taller or shorter than the child being measured.