By the time they start school, wealthy kids are already five months ahead in learning skills, have wider vocabularies and fewer behavioural problems.
The Resolution Foundation think tank, which analysed data on 15,000 children who turned five in 2006, found wealthier parents were able to create a "richer learning environment" for their children.
For example they found that 75 per cent of higher-income children were read to daily aged three, compared with 62 per cent of children in low to middle-income households. While 42 per cent of more affluent children visited a library at least once a month; this figure was 35 per cent for worse off families.
Mothers in low to middle-income groups were at greater risk of post natal depression and had lower self-esteem and less sense of control over their lives, they said.
The research said the lag in attainment by the less wealthy groups could also be explained by their parents' age and qualifications.
Low and middle-income group parents – those earning between £24,000 and £42,000 - were three times more likely to have no formal qualifications beyond GCSE.
Vidhya Alakeson, director of research at the Resolution Foundation, said the problems faced by children in this group were not as bad as those in the lowest income groups, but they should be taken seriously, as there was a danger that without support some in this group could fall further behind.
She said "policy makers rightly focus on trying to improve outcomes for children in the very poorest families... but this new study shows the perils of ignoring the low to middle group who are a third of our future workforce.
"With parents increasingly squeezed for time and money, this only creates more stress and even less positive environments for their children."
Ms Alakeson told the BBC she wants the Government to ensure there are no further cuts to tax credits which have had a big impact on lower-income families. She wants employers to be encouraged to allow working parents as much flexibility as possible.
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