In 1951, a renowned American psychologist wrote the following:
"What factors in a child's background and environment are associated with the rapid development of speech? Girls have a slight advantage over boys in their speed of development in nearly all the aspects of language that have been studied. ...Children in families with low incomes tend to be neglected, and their linguistic retardation is the most noticeable aspect of their generally retarded development. Children in more favored homes develop speech much faster. Children who are associated primarily with adults develop rapidly, and thus single children outstrip children with many brothers and sisters. Children from multiple births and children from polylingual homes are often retarded."
Who is he?
Hint: The title of the paper he's famous for contains the word "magical." (Dead giveaway, yes?)
Brownie points if you can identify which of these views have withstood the test of time and which have not.