A Brief History of IQ Testing
The first modern intelligence test was developed by Alfred Binet and Théodore Simon in 1905, commissioned by the French Ministry of Public Instruction to identify schoolchildren who needed special educational support. Binet was explicit that his scale measured a child's current cognitive performance, not innate or fixed capacity.
The first modern intelligence test was developed by Alfred Binet and Théodore Simon in 1905, commissioned by the French Ministry of Public Instruction to identify schoolchildren who needed special educational support. Binet was explicit that his scale measured a child's current cognitive performance, not innate or fixed capacity, and he warned against treating the scores as anything more than a screening tool.
The Binet-Simon scale was translated into English by Henry Goddard at the Vineland Training School in 1908, and revised by Lewis Terman at Stanford in 1916, producing the Stanford-Binet — the first IQ test widely used in the United States. Terman's interpretation of the scores was substantially less cautious than Binet's: he treated IQ as a measurement of innate capacity, and his work supported the eugenic policies that dominated American educational and immigration policy through the 1930s.
The First World War accelerated IQ testing's adoption. Robert Yerkes and a team of psychologists developed the Army Alpha (for literate recruits) and Army Beta (for illiterate or non-English-speaking recruits) to triage 1.7 million American draftees. The Army results were published in heavily-criticized form in the 1920s and were used to argue for restrictive immigration laws, despite serious methodological flaws including substantial cultural and educational confounding.
David Wechsler, working at Bellevue Hospital in New York, published the first version of his Wechsler-Bellevue Intelligence Scale in 1939. The Wechsler scales introduced two crucial innovations: the deviation-IQ scoring system (replacing Binet's mental-age ratio) and the structure of multiple subtests yielding both a full-scale IQ and separate verbal and performance index scores. The Wechsler family of tests — WAIS for adults, WISC for children, WPPSI for preschoolers — has dominated clinical IQ assessment ever since.
The post-war period brought serious reckoning with the cultural assumptions baked into mid-century IQ tests. The 1969 Jensen controversy and the 1994 publication of 'The Bell Curve' both renewed public debate about the meaning of group differences in IQ scores. The American Psychological Association's 1995 task force report, 'Intelligence: Knowns and Unknowns', remains the most-cited summary of the consensus view: IQ tests measure something real and predictively useful, but the meaning of any particular score depends heavily on the conditions under which it was obtained.