Today anyone can take an online “IQ test” in twenty minutes. Yet the history of testing began not with a wish to rank people but with a practical question: how do we find the children who need extra help? The search for an answer took almost a hundred years and was full of mistakes and discoveries.
Before Binet: from doctors to laboratories
In 1838 the French physician Jean-Étienne Esquirol separated intellectual disability from mental illness and treated the use of language as the main criterion for identifying it. In England, Francis Galton, Charles Darwin's half-cousin (they shared a grandfather), published Hereditary Genius in 1869. He measured simple sensory abilities, such as keenness of sight and hearing and speed of reaction. Galton showed that many human traits follow the normal distribution, the familiar bell-shaped curve, and used correlation to compare them. He was also among the first to use questionnaires and rating scales. But Galton believed abilities were almost entirely inherited, a strong assumption that is not accepted today.
In 1879 Wilhelm Wundt opened the first psychology laboratory. He treated individual differences as measurement error, but he showed that mental processes can be measured. In 1890 the American psychologist James McKeen Cattell coined the term “mental test”. His sensory tests, however, could not predict who would do well at school.
Binet and Simon: a test to help
In 1895 the French psychologist Alfred Binet, together with Victor Henri, proposed measuring not simple sensations but the higher functions of the mind — memory, imagination, attention and understanding. In 1904 the French education ministry set up a commission to find a way of identifying pupils who needed extra help. For this purpose Binet and the physician Théodore Simon created the first intelligence scale in 1905: 30 tasks, from easy to hard, tried out on 50 children aged 3 to 11.
In 1908 the authors grouped the tasks by age, from 3 to 13, and in 1911 they revised the scale again. This gave rise to the idea of mental age: if a child can do the tasks that 8-year-olds usually manage, their mental age is 8, whatever their actual age.
Binet himself warned that a test result is provisional: it shows the child's present state, not their destiny, and mental abilities can be developed through practice and good teaching. He created the test to help, not to label.
From mental age to IQ
In 1912 the German psychologist William Stern proposed dividing mental age by actual age — and so the intelligence quotient (IQ) was born. In 1916 Lewis Terman of Stanford University adapted Binet's scale for the USA (the Stanford–Binet) and multiplied the ratio by 100. For example, a child of 8 with a mental age of 10 has an IQ of 125.
In 1917, when the USA entered the First World War, large numbers of recruits had to be tested quickly. This led to the first group tests: the written Army Alpha and the picture-based Army Beta for those who could not read well. Now dozens of people could be tested at once with paper and pencil.
In 1939 David Wechsler introduced a new scale with two parts: verbal (for example, comprehension and arithmetic) and performance (for example, building patterns from blocks and putting pictures in order). Most importantly, he dropped mental age, which did not suit adults, and introduced the deviation IQ: a person's result is compared with the results of people of the same age. The average is 100; about 68% of people score between 85 and 115, and about 95% between 70 and 130. A children's version (WISC) followed in 1949.
Tests around the world
Tests were soon adapted for other languages and countries. In Egypt, for example, local tests were developed from the 1930s, and Arabic versions of the Stanford–Binet appeared in 1938 and 1956. Experience showed that simply translating a test is not enough: the tasks must suit the children's language and culture, and the norms — the average results for each age — must be set in that same country. Norms also go out of date: in 1984 James Flynn showed that average scores in the USA had been rising by about 3 points per decade. That is why tests need to be re-normed regularly.
What this history teaches us
Intelligence tests were invented to help children who need support, and that remains their best use. For parents and teachers, this history offers a few lessons: - A test result is provisional — Binet already said so. It shows today's situation, not a life sentence. - A test shows only what it measured. Ask which abilities were assessed, which test was used and whether its norms suit children like yours. - A good test is both reliable (its results are stable) and valid (it really measures what it is meant to). - The most important question after any test is: how are we going to help the child now?