The Wechsler scale, introduced in 1939, provides a verbal and performance measure.

Both of these tests yield an I.Q. score that expresses an individual's intelligence compared with a representative group of people of the same age, with the average IQ set at 100. For example, if a 14-year-old does as well as the average 16-year-old, he earns a mental age of 16. This is divided by the child's chronological age (14) and multiplied by 100 to arrive at the IQ score. In this case, the child's I.Q. is an above-average 114 (16/14*100=114).