There are many forms of unfairness in life and this is just one. This is the title Socioeconomic status and the growth of intelligence from infancy through adolescence and here is the abstract:

Low socioeconomic status (SES) children perform on average worse on intelligence tests than children from higher SES backgrounds, but the developmental relationship between intelligence and SES has not been adequately investigated. Here, we use latent growth curve (LGC) models to assess associations between SES and individual differences in the intelligence starting point (intercept) and in the rate and direction of change in scores (slope and quadratic term) from infancy through adolescence in 14,853 children from the Twins Early Development Study (TEDS), assessed 9 times on IQ between the ages of 2 and 16 years. SES was significantly associated with intelligence growth factors: higher SES was related both to a higher starting point in infancy and to greater gains in intelligence over time. 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. Although these key results did not vary across girls and boys, we observed gender differences in the development of intelligence in early childhood. 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.

This is the news report to help you understand the point: Does poverty impact intelligence? Deprived children are 6 IQ points worse off than wealthy peers – and the gap widens with age.

Poverty affects the intelligence of children as young as two, a study has found – and its impact increases as the child ages.

Deprived young children were found to have IQ scores six points lower, on average, than children from wealthier families.

And the gap got wider throughout childhood, with the early difference tripling by the time the children reached adolescence. . . .

The results, published in the journal Intelligence, revealed that children from wealthier backgrounds with more opportunities scored higher in IQ tests at the age of two, and experienced greater IQ gains over time.

Dr Sophie von Stumm, from Goldsmiths, University of London, who led the study, said: ‘We’ve known for some time that children from low socioeconomic status (SES) backgrounds perform on average worse on intelligence tests than children from higher SES backgrounds, but the developmental relationship between intelligence and SES had not been previously shown.

‘Our research establishes that relationship, highlighting the link between SES and IQ.

‘We hope that our findings will drive future research into the specific mechanisms and factors that underpin the link between SES and IQ and thus, contribute to widening the IQ gap.’