[Tax-chick]

Studies show that children whose parents have professional careers speak nearly twice as many words per hour to them as children with working class parents — and several times as many words per hour as children in families on welfare. There is no way that children from these different backgrounds are going to have equal chances of economic or other success in adulthood.

He left out the connection between the facts and the conclusion, here. "Studies show" (wizard words ;-) that a child's school success can be predicted based on the number of words the child understands when he starts school. Verbal comprehension is both in itself a key academic ability, and a marker for a whole array of factors that contributed to academic success.

[KC Burke]

He keeps his columns very non-technical for the general reader. As his detailed books on Late Talking Children would stress, he very well understands all the detailed distinctions, he just did not want to “go into the weeds” while making his broader point in straight forward prose.