Charts relating weight, height and head circumference to age have been devised, and give an indication of the normal rate of growth, particularly in childhood. (See APPENDIX 6: MEASUREMENTS IN MEDICINE for more details.) The wide variation in normal children is immediately apparent on studying such charts. Centile or percentile charts describe the distribution of these characteristics in a population. They are obtained by taking measurements of a large population of each sex at each age. For each age there will be a height, above and below which 50 per cent of the population lies: this is called the 50th centile. The 50th centile thus indicates the mean height at a particular age. Such tables are less reliable around the age of PUBERTY, because of variation in age of onset.

Minor variations from the mean do not warrant investigation, but if the height of an individual falls below the third centile (3 per cent of normal children have a height that falls below this) or above the 97th centile, investigation is required. Changes in the rate of growth are also important, so if a child's measurements deviate away from the original centile lines on which they were situated, investigations may be necessary. Skeletal proportions may provide useful information. There are many children who are normal but who are small in relation to their parents; the problem is merely growth delay. These children take longer to reach maturity and there is also a proportional delay in their skeletal maturation – so that the actual height must always be assessed in relation to maturity. The change in skeletal proportions is one manifestation of maturity, but other features include the maturing of facial features with the growth of nose and jaw, and dental development. Maturity of bone can readily be measured by the radiological bone age.

Failure to gain weight is of more significance. Whilst this may be due to some underlying disease, the most common cause is a diet containing inadequate calories (see CALORIE). Over the last six decades or so there has been quite a striking increase in the heights and weights of children in the developed world, with manufacturers of children's clothing, shoes and furniture having to increase the size of their products. Growth is now completed at 20–21 years, compared with 25 at the beginning of the 20th century. It has been suggested that this increase, and earlier maturation, have been due to a combination of genetic mixing as a result of population movements, with the whole range of improvement in environmental hygiene – and not merely to better nutrition.