This number struck me as unbelievably large when I first heard it, so I looked into it here: http://skeptics.stackexchange.com/questions/20139/do-poor-children-

This number struck me as unbelievably large when I first heard it, so I looked into it here: http://skeptics.stackexchange.com/questions/20139/do-poor-children-hear-30-million-fewer-words-by-age-3 http://skeptics.stackexchange.com/questions/20139/do-poor-ch... tl;dr I think 30 million is an overestimate.