The long term trend is quite extraordinary with regard to the total number going into higher ed (which form networks too, although not the same as the elite institutions).
"Two percent of Americans aged 18 to 24 were enrolled in a university at the beginning of the 20th century. At nearly the end of the 20th century, beyond 60 percent, or 14 million students, were enrolled in 3500 four year or two year colleges."
"Two percent of Americans aged 18 to 24 were enrolled in a university at the beginning of the 20th century. At nearly the end of the 20th century, beyond 60 percent, or 14 million students, were enrolled in 3500 four year or two year colleges."
http://ajha.org/early-history-of-universities-in-america.htm