"If intelligence were deeply encoded in our genes, that would lead to the depressing conclusion that neither schooling nor antipoverty programs can accomplish much."

More optimistically, it means that they're already working pretty well. In a chaotic environment where smart people are likely to be randomly struck down, most variation in intelligence is environmental: The smartest are those who avoid malnutrition, neonatal infections, mothers with drug addictions, etc. In a utopia where everyone receives perfect education and lives up to their full innate potential, all variation is due to genetics, because we're holding everything else constant.

Edit: Less optimistically, it also means that there are no additional gains to be had at the margin. Maybe the benefit of public schooling has been just to sort smart-student pegs into high-paying-job holes, and now that most of that sorting is done there's nothing left for schools to do.