How can I tell if a child’s height is developing normally? To determine whether a child’s height is normal, we must first compare the height of the child with that of a normal healthy child of the same age and sex. This normal height is called standard deviation, which is a number calculated from the physical measurements of a large number of representative healthy children, and is generally used to express the growth level of children by the standard deviation method and the percentile method. The standard deviation method uses the mean and standard deviation as the “standard of difficulty” for evaluation. Any height within the mean plus or minus 1 standard deviation is medium, within the mean plus or minus 2 standard deviations is medium to high, more than 2 standard deviations is high, and below the mean minus 2 standard deviations is low, and is short. The percentile method is to rank the height of 100 people in order from smallest to largest, and those ranked from 25th to 75th are medium, those ranked from 75th to 97th are upper-middle, those ranked above 97th are upper, those ranked from 25th to 3rd are lower-middle, and those ranked below 3rd are lower and belong to short stature. Since there are obvious differences in the growth of different races and regions, the recent physical development figures representing the country and nation should be chosen as the evaluation standard. It is worth noting that the above-mentioned standard values can only determine the position of a child’s height in the population, and to determine whether it is abnormal or not, it is necessary to consider the family’s height and weight. To determine whether a child is abnormal, the influence of family factors should be considered. For example, a child whose height is at the 10th percentile and whose parents are at the 90th percentile and are tall, will have abnormal height development even though his or her height is in the normal range. If the child’s height is at the 3rd percentile and his/her parents’ height is also at the 3rd percentile, his/her growth is normal and he/she is familial short stature. Therefore, the influence of parental height on a child’s height should be taken into account when evaluating the child’s height. The average height of the parents is the adult height of the child as determined by the genetic potential, also known as the target height. The following formula can be used to calculate a child’s target height: Boy height (cm) = [father’s height + (mother’s height + 13)]/2±7.5 Girl height (cm) = [(father’s height – 13) + mother’s height]/2±6 If a child’s height is not within the percentile curve of the expected target height, a search for the cause is needed. Therefore, it is helpful to combine parental height when using growth scales to infer whether a child’s height is normal. For pubertal children, a combination of indicators such as sex development and bone age is also needed.