The Measurement of Intelligence: An Explanation of and a Complete Guide for the Use of the Stanford Revision and Extension of the Binet-Simon Intelligence Scale

Terman's central claim is that intelligence is a largely innate, hereditary capacity that can be measured with sufficient precision to assign each child a stable numerical score—the Intelligence Quotient. He rejects the view that mental ability is primarily shaped by environment or education, and he rejects the Binet-Simon scale's original emphasis on identifying children needing remedial instruction in favor of a tool for classifying the entire school population. The book argues that IQ testing should become a routine instrument of educational administration, sorting children into tracks and identifying the 'feeble-minded' for institutional segregation.

The book standardized the Intelligence Quotient (IQ) as a ratio of mental age to chronological age, multiplied by 100, and provided the first large-scale American normative sample for administering the test. While William Stern had proposed the IQ formula, Terman's manual made it operational for mass testing. The Stanford Revision introduced several new items, revised scoring criteria, and, crucially, established age norms based on testing approximately 1,000 California children. This became the template for virtually all subsequent individually administered intelligence tests in the United States.

Binet and Simon designed their scale as a diagnostic aid for identifying Parisian schoolchildren who needed special education, with no claim that the score measured fixed, innate intelligence. Terman reversed this orientation. He emphasized the hereditarian interpretation, added items suited to American cultural context, extended the scale's range upward to 'superior adults,' and reframed the test's purpose as sorting children by native ability. Where Binet warned against reifying intelligence as a single measurable quantity, Terman embraced exactly that reification.

Terman's hereditarian confidence has been substantially undermined. Twin and adoption studies since the mid-twentieth century show substantial environmental effects on IQ scores, and the heritability estimates Terman assumed have been revised downward for children and complicated by gene-environment interactions. The specific racial and class hierarchies Terman asserted—that intelligence deficiency was 'very, very common among Spanish-Indian and Mexican families' and 'negroes'—are now understood as reflecting test bias, educational inequality, and the cultural specificity of test items, not innate differences. The book remains historically important but its central interpretive claims are rejected by mainstream psychometrics.

The book is often cited as if it merely adapted Binet's test for American use, glossing over Terman's aggressive transformation of its purpose and his explicit eugenic program. A common oversimplification treats the Stanford-Binet as a neutral scientific instrument that was unfortunately misapplied by later racists, when in fact Terman's manual embedded hereditarian and nativist assumptions into the test's administration, scoring, and interpretation from the outset. The book's promotion of testing for 'feeble-minded' classification directly contributed to sterilization laws and immigration restriction in the 1920s.

Walter Lippmann, writing in The New Republic in 1922, mounted the most prominent contemporary critique, challenging the scientific pretensions of IQ testing and arguing that Terman and his allies had turned a fallible instrument into a dogmatic measure of human worth. Lippmann questioned whether intelligence could be reduced to a single number and warned that the tests would be used to justify social inequality. In response, Terman dismissed Lippmann as a journalist unqualified to judge psychological science, but the exchange exposed the gap between the test's practical appeal and its theoretical justification.