Who Invented the IQ Test?

Quick Answer

Alfred Binet, with Théodore Simon, created the first practical intelligence test in Paris in 1905 — built to identify schoolchildren needing educational support, not to rank the general population. William Stern coined the term IQ in 1912, Lewis Terman's 1916 Stanford-Binet standardized it in America, and David Wechsler's 1939 scales established the modern scoring system.

The Four Founders

Binet's 1905 test introduced age-graded tasks and the concept of mental age. He was emphatic that his instrument measured current performance, not fixed capacity — a warning history mostly ignored. Stern contributed the quotient formula (mental age ÷ chronological age × 100), giving the score its name.

Terman adapted and standardized the test at Stanford, launching mass testing — including the US Army's WWI screening of 1.7 million recruits, which normalized cognitive testing at scale. Wechsler, dissatisfied with the Binet's adult validity, built the Wechsler-Bellevue in 1939 and introduced deviation scoring against age-group norms, the system every major test still uses.

The Complicated Legacy

The same instruments that expanded educational opportunity were also enlisted, particularly in the 1910s–30s, to justify eugenic policies and discriminatory immigration quotas — applications Binet himself would have rejected and that modern psychology explicitly repudiates. Understanding that history is part of using these tools responsibly.

Modern tests bear little surface resemblance to Binet's: they're normed on stratified national samples, screened item-by-item for bias, and interpreted with confidence intervals and subtest profiles rather than a single verdict. But the core insight — that reasoning ability can be sampled and compared systematically — remains Binet's.

Frequently Asked Questions

When was the first IQ test created?

1905 — the Binet-Simon scale, developed by Alfred Binet and Théodore Simon for the French education ministry to identify children needing additional support.

What was the original purpose of IQ testing?

Educational triage, not ranking: Binet designed his test to find struggling schoolchildren so they could receive help. He explicitly warned against treating scores as a measure of fixed, innate intelligence.

How is the modern IQ test different from Binet's?

Modern tests use deviation scoring against age-group norms (not mental age), sample multiple ability domains, are normed on representative national samples, and undergo statistical bias screening — plus they're revised roughly every decade to stay current.