Stability and Change in Human Characteristics

Bloom synthesized data from eight major longitudinal studies, including the Harvard Growth Study, Berkeley Growth Study, and California Growth Study, supplemented by Terman's Genetic Studies of Genius and other follow-up investigations . His method was to compare correlations between measurements taken at different ages and to estimate the proportion of mature development achieved at each age level. The book examined physical characteristics, intelligence, academic achievement, interests, attitudes, and personality. Bloom's key finding was that development follows a negatively accelerated curve: it is most rapid in early childhood and slows progressively. This pattern, he argued, means that environmental influences have their greatest effect during periods of rapid development, making early childhood the critical window for intervention.

Bloom's research showed that 50 percent of the variation in adult intelligence could be predicted by age 4 and 80 percent by age 8, and that early home experiences shaped later learning ability [citation:4][citation:8]. These findings focused attention on early education and the home environment. Bloom discussed his research with President Lyndon B. Johnson and testified before Congress during national debates about educational opportunity for disadvantaged children [citation:4]. Lorin Anderson, a former student, stated that Bloom 'provided the intellectual and empirical basis for Head Start' [citation:4]. The program was established in 1965 as part of Johnson's Great Society, providing education, health, and nutrition services to low-income children and families [citation:4][citation:8].

Critics challenged both Bloom's method and his conclusions. Wayne Dennis, reviewing the book in Contemporary Psychology, noted that all data had been reviewed in earlier publications and no new data were reported. He questioned whether growth in height provided a good model for stability and change in behavior, and disagreed that Bloom had shown the social sciences could draw 'powerful generalizations' [citation:15]. John Holt, writing in The New York Review of Books, argued that Bloom's tables showed only what was happening under existing conditions, not what might be possible under different ones. Holt contended that the stability of IQ in conventional schools reflected the schools' failure to foster intelligence, not an inherent limit on development [citation:10].

Bloom's concept of stability was developmental, not fatalistic. He argued that characteristics with an underlying structure or pattern—general intelligence, academic achievement, basic personality—tend to remain stable unless that underlying structure is changed [citation:20]. However, he explicitly distinguished the underlying structure from its mode of expression: aggressiveness may arise from a stable personality makeup but be expressed differently at ages 4 and 16 [citation:20]. The stability Bloom documented was observed under existing environmental conditions, not proof of immutability. Critics like Holt and Bettelheim read his findings as evidence that early deprivation permanently forecloses development, a conclusion Bloom himself rejected. His data, he argued, made the case for early intervention, not despair.

The two works address different stages of the educational process. Taxonomy of Educational Objectives (1956) provided a classification of cognitive goals—knowledge, comprehension, application, analysis, synthesis, evaluation—that helped educators specify learning outcomes [citation:8]. Stability and Change (1964) examined the developmental conditions under which those outcomes are achieved, arguing that early experience shapes the capacity for later learning [citation:4]. The relationship is one of complementarity: the Taxonomy told educators what to teach; Stability and Change told them when and why early intervention matters. Both reflect Bloom's lifelong focus on the conditions that enable all children to learn at high levels, a theme he developed further in All Our Children Learning (1980) [citation:11].

Bloom's conclusion was that environment determines the extent and kind of change in a characteristic. He distinguished between characteristics like height, which are largely genetically determined but environmentally enabled or blunted, and school achievement, which is more clearly determined by environment [citation:20]. His key finding was that the magnitude of change in a given period correlates with the environment, not with the initial measure of the characteristic. This means that during periods of rapid development, environmental variation produces the greatest differences in outcomes. Bloom did not claim that intelligence is fixed; he claimed that it develops most rapidly early, and that this makes early environmental conditions disproportionately consequential [citation:20].