Jensen is a controversial figure, largely for his conclusions based on his and other research regarding the causes of race based differences in intelligence and in this book he develops more fully the argument he formulated in his controversial Harvard Education Review article 'How Much Can We Boost IQ and Scholastic Achievement?'. In a wide-ranging survey of the evidence he argues that measured IQ reveals a strong hereditary component and he argues that the system of education which assumes an almost wholly environmentalist view of the causes of group differences capitalizes on a relatively narrow category of human abilities.

Since its original publication the controversy surrounding Jensen's ideas has continued as successive generations of psychologists, scientists and policy-makers have grappled with the same issues.