Just throwing this out there:

"Specifically, children from low SES families scored on average 6 IQ points lower at age 2 than children from high SES backgrounds; by age 16, this difference had almost tripled. ... Overall, SES was shown to be associated with individual differences in intercepts as well as slopes of intelligence. However, this finding does not warrant causal interpretations of the relationship between SES and the development of intelligence." [1]

[1] Socioeconomic status and the growth of intelligence from infancy through adolescence https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4641149/