The development of testing procedures has been based on the assumption that the greater proportion of ability is inherited. Tests are therefore designed to measure innate ability, while controlling for environmental and cultural factors. Many critics, however, claim that it is not possible to achieve this aim, and that test results remain culturally biased towards the norms and values of dominant groups in society. According to this view intelligence tests therefore fail to reflect the true intelligence levels of subordinate class, race or gender groups.
The educational and political significance of intelligence testing can be seen in the fierce reaction to Jensen's reopening of the NATURE–NURTURE DEBATE in 1969 (see L. Kamin, The Science and Politics ofI.Q.). Jensen's claim that 80% of intelligence was due to genetic factors was followed with even more controversial arguments attributing a significant proportion of the lower test performance of American blacks to this cause. Test results were therefore suggested as legitimizing the differential educational treatment received in schools by different social groups.
Within the field of education, educationists have often argued that concentration on intelligence testing and the automatic equation of a high IQ score with brightness and achievement have straitjacketed the education system for over half a century (e.g. the effects of 11+ in allocating children to different types of educational provision and experience). Others have consistently defended the predictive powers of IQ tests. Currently there tends to be more agreement that tests are neither wholly neutral nor wholly valid (see VALIDITY), but they remain a useful diagnostic tool in the assessment of cognitive and learning difficulties.