From Science Daily:

The winner of a decades-old debate about what scientists call the fadeout effect — one of the most persistent research mysteries in intelligence and psychological development — may finally have been decided.

Following a meta-analysis of experimental methods to determine whether or not the benefits of early interactions designed to raise intelligence remain over time, UC Santa Barbara postdoctoral researcher John Protzko found that the positive effects on intelligence actually diminish after a particular intervention ends. Protzko’s study marks the first quantitative analysis of the fadeout effect across nearly every known intervention that has attempted to improve early intelligence.

The findings, which appear in the journal Intelligence, have important implications for the long-term benefits of programs such as Head Start, a federal initiative that promotes school readiness of children under 5 from low-income families through education, health, social and other services.

“Many theories of cognitive development and the relationship between the environment and intelligence are not able to account for the fadeout effect,” said Protzko, who is a member of the META (Memory, Emotion, Thought, Awareness) Lab in the Department of Psychological & Brain Sciences at UCSB. “Reciprocal interaction models, for example, put forward that no such fading would occur. It turns out that when you raise children’s intelligence, they may not go out and select into new, more cognitively demanding environments. Other traits may be driving what environments children select into.”

The 44 randomized controlled trials that Protzko analyzed for the study included a total of 7,584 young children.…

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