Who Invented the IQ Test?

Who invented the IQ test? Meet Alfred Binet & Théodore Simon – the French duo who created the world’s first successful IQ test in 1905! Discover their story and who shaped modern IQ testing.

Dr. Russell T. WarneChief Scientist

The first successful intelligence test was created by Alfred Binet and Theodore Simon in Paris in 1905. While others had attempted to measure intelligence before them, Binet and Simon were the first to create a test that actually worked.

The Context Behind the First IQ Test

In the early 1900s, France was grappling with how to educate children with special needs. Alfred Binet, a psychologist who had spent years studying cognitive development, believed these children deserved education in schools, not confinement in psychiatric facilities.

Binet partnered with Theodore Simon, a young physician, to create a test that could identify children who might struggle in regular classrooms. Their 1905 test consisted of 30 questions arranged in order of difficulty, ranging from simple commands to complex problems requiring reasoning and judgment. What made it revolutionary was that it actually predicted which children would struggle academically, which is something earlier attempts had failed to do.

Binet and Simon published improved versions in 1908 and 1911 (the year Binet died). The tests became wildly popular and were quickly translated into German, Italian, English, and other languages.

Alfred Binet

Failed Attempts Before Binet

Binet wasn't the first to try measuring intelligence. The most notable earlier attempt came from Sir Francis Galton, who set up a laboratory in London during the 1880s. Galton believed intelligence was related to physical traits, and so he measured head circumference, grip strength, reaction time, visual acuity, and other variables he believed were the product of simple processes in the nervous system.

After years of collecting data, Galton found essentially no relationship between these measurements and social class. With modern knowledge, we now know that some variables do relate to intelligence (reaction time actually correlates with IQ), but his methods were not sophisticated enough to detect these relationships.

Lewis Terman and the Stanford-Binet

Lewis Terman, a professor at Stanford University, expanded Binet's work significantly. In 1916, he published the Stanford-Binet Intelligence Test, which covered a wider range of intelligence levels and could be used with different ages, though its primary examinee population was still children. The Stanford-Binet became the gold standard for intelligence testing in the United States, and a modern version is still used today.

The Army Alpha and Army Beta

Shortly after publishing the Stanford-Binet, Terman joined a committee that worked with the U.S. Army during World War I. Because of the draft, the number of men joining the army had increased dramatically in a short time. The committee’s goal was to create a test that could quickly identify men who would be unsuitable for military service and to identify potential leaders. Individual testing was impractical.

The committee’s solution was revolutionary: tests that could be administered to large groups simultaneously. The committee developed the Army Alpha for literate soldiers and the Army Beta for those with limited literacy. Over 2 million tests were administered before the war ended, proving that mass testing was possible and that IQ scores mattered for adults beyond school settings.

David Wechsler's Contributions

David Wechsler introduced several important innovations starting in 1939. He created the deviation IQ score (which solved mathematical problems with the original quotient formula) and separate verbal and nonverbal scores to provide more nuanced information.

Modern versions of Wechsler's tests, such as the WAIS (Wechsler Adult Intelligence Scale), WISC (Wechsler Intelligence Scale for Children), and WPPSI (Wechsler Preschool and Primary Scale of Intelligence), are the most widely used individually administered IQ tests today.

Learn more about the History of IQ Tests here.

Why Binet's Innovation Mattered

Alfred Binet and Theodore Simon deserve credit as the inventors of the IQ test because their success created a template that later test creators could follow. In fact, some of their test creation principles -- such as comparing examinees to their age peers -- are still part of intelligence testing today. Every IQ test created since 1905 owes a debt to Binet and Simon's original insights.

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