http://pss.sagepub.com/content/14/6/623.short

http://dl.dropboxusercontent.com/u/67168735/heritability%20of%20iq.pdf

"Socioeconomic status modifies heritability of IQ in young children".

To make a long story short, this analysis of a large cohort of children assigned a 'socioeconomic status indicator' to each family they were following from 0 to 100 based on a large number of factors. They found that the heritability of IQ was a VERY strong positive function of socioenomic status. At the bottom, they think less than 5% of IQ variation is moderated by genetics. At the top of the scale, over 80%.

Obvious interpretation: low socioeconomic status masks genetic predisposition.