Going to a $200,000 family income from a $1,000 family income raises the score only to the 76th percentile from the 50th—an increase of 26 percentiles.
1) Notice the wording which implies correlation means causation: "... family income raises the score..."
2) Interesting as some wealthy families who own their family business have paid themselves $0 annual salary, to gain financial advantage.
Beyond $200,000, PIAT scores go down as income increases.
Obviously, capping salaries at 200K USD would raise the intelligence of the kids whose parents are plagued by excessive salary. To aid in redistribution, why not cap salaries at 125K USD!
Some may say it is the
behaviors which tend to lead to educational, academic, and career achievements... and that the behaviors reveal the broad range of underlying
values, such as work ethic, held by different families.
People love a rags-to-riches success story, championing the underdog is part of the American dream. Many find the story of Dr. Ben Carson, "Gifted Hands" to be highly inspirational. His mom was divorced, had only a third grade education, was functionally illiterate, but possessed great dignity and worth ethic. In limiting her sons' TV viewing and encouraging use of the local public library, she raised their expectations of what their lives could be.
Some may say that a problem with dire reports about correlation between SES and achievement is that such reports may tend to become a negative self-fulfilling prophecy... an excuse for not pushing the boundaries and creating opportunity where there was none. 
