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Studies of infants placed in orphanages who were later exposed to family rearing showed significant differences in this domain of development based on whether they were adopted before the age of 6 months or after that time.
What is cognitive development? (For children adopted before 6 months, cognitive catch-up was significant by early childhood and adolescence; for those institutionalized longer than 6 months, more serious intellectual deficits were observed, and while there was some improvement over time, they remained substantially below average.)