Skodak, M. (1939). The mental development of children placed in foster homes under the age of six months. In M. Skodak, University of Iowa studies: Studies in child welfare: Vol. 16. Children in foster homes: A study of mental development (pp. 37-105). Iowa City, IA, US: University of Iowa.
http://dx.doi.org/10.1037/13499-003
Children who are born in established families and who grow up in the same homes follow certain fairly well established patterns in mental development. A certain degree of relationship has been found between the intelligence of siblings born of the same parents and reared in the same homes, and between the intelligence of the children and the parents. Since both the factors of heredity and environment influence mental development under these conditions, the study of children in their own homes can yield little information on the possible effectiveness of home environment on mental development. Studies of the relationship between such factors as occupational classification of the parents and the intelligence of the children reveal present status, it is true, but cannot give a causal explanation. It has been shown repeatedly that children from the lower socio-economic levels are, in general, inferior to those from higher levels in intelligence and this is usually attributed to the inferiority of the parents. But are the parents of children in the lower socio-economic classes in these classes because they are innately incapable of rising to higher levels, or are the parents incapable of rising to higher levels because they lacked the stimulation and opportunities for greater development in the inadequate homes of their own parents? No amount of sequential study of children in their own homes can answer this problem. The experimental situation consists of placing infants of known underprivileged family backgrounds into homes known to be average or above average in terms of certain criteria, where the children will be raised as essential members of the family, having known no other environment. (PsycINFO Database Record (c) 2016 APA, all rights reserved)