Theories of generalized intelligence often assume that intelligence can be measured by testing and that it is a fixed trait. However, just as the concept of general intelligence itself was debated, so also was the emphasis placed upon its genetic basis. Studies showed that environmental factors play an important role, and interventions can improve test scores.
The Milwaukee project in 1969 involved 40 families from a disadvantaged part of the inner city. Mothers of very young children were offered classes to help them improve their economic and social status. When they went back to school, their children had an above-average IQ compared to those who did not receive such help. However, after finishing school, the children’s IQ levels fell back to the level typical of the area.
