Skeels and Dye (1939) transferred 12 children under 3 years of age from an orphanage to an institution for individuals with intellectual disabilities. In the institution, the children were cared for with great affection by adolescent girls who were considered to have intellectual disabilities. A comparison group of children remained in the orphanage, where they received no specialized attention. Follow-up testing demonstrated that the intelligence scores of those placed in the stimulating environment increased, whereas those of the children who remained in the orphanage decreased (Skeels,
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