How did IQ tests become connected to scientific racism in the United States?

The connection between IQ tests and scientific racism in the United States emerged as psychologists adopted and reinterpreted early intelligence tests. While psychologist Alfred Binet initially developed tests in France to help children with learning difficulties, not to create hierarchical groupings, American psychologists adapted these tests for use in the U.S. Lewis Terman and his colleagues at Stanford University created the Stanford-Binet IQ test, which became a standard.

During the early 20th century, a prevailing belief in heredity and a racial worldview led many Americans to believe intelligence was innate and unchangeable. IQ tests were administered widely, and their results often confirmed the expectations of white Americans, as Black individuals, on average, scored lower than white individuals. This was interpreted as evidence of inherent racial differences in intelligence, aligning with the concept of biological determinism.12

However, critics pointed out that intelligence was not clearly defined and that tests could be culture-bound, reflecting the cultural experiences and education of test-takers rather than innate ability. Research in the 1930s by psychologist Otto Klineberg, for instance, showed that Black test-takers in Northern states with better educational funding performed better than white test-takers in Southern states with lower educational expenditures, suggesting a correlation between socioeconomic factors and IQ scores. Despite these critiques, aspects of scientific racist thought, including the misuse of IQ testing, have persisted.134