Poverty affects the IQ of children as young as two and has an impact that increases with age, according to psychologists.
A UK study shows that deprived young children have IQ scores about six points lower those from high socio-economic status families.
The gap widens throughout childhood with the early difference tripling by the time children reach adolescence.
The scientists looked at data on almost 15,000 children and their parents as part of the Twins Early Development Study which is investigating socio-economic and genetic links to intelligence.
Children were assessed nine times from the ages of two to 16 using a mixture of parent-administered, web and telephone-based tests.
The results, published in the journal Intelligence, showed that children from more advantaged backgrounds scored better at age 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."