Children from the poorest families are almost a year-and-a-half behind the richest children in vocabulary tests by the time they reach school age, research has found.The study from the Sutton Trust, an education think-tank, found that inequalities in knowledge were already apparent before children started school.

Sir Peter Lampl, chairman of the trust, which campaigns for equality of opportunity in education, said: “It is a tragic indictment of modern society that our children's future life prospects depend so much on their family background, not their individual talents.”

The trust responded by calling for more help for children from poor backgrounds. Its suggestions, which it argued would not add to pressure on public spending, included taking funds aimed at extending free nursery education among three- and four-year-olds, and using them instead to give 25 hours a week of nursery education to two- to four-year-olds from families in the poorest 15 per cent.

The research suggests that low income in itself makes some difference to children's educational level through lack of access to opportunities afforded by, for example, a car.

However, the same research also indicates that some parenting styles associated with but probably not caused by low income help explain the gap between the knowledge of poor children and other young people. For example, only 45 per cent of children from the poorest fifth of families were read to daily at the age of three, compared with 78 per cent of children from the richest fifth of families. Many studies find regular reading with a parent enlarges a child's vocabulary.

Lee Elliot Major, research director, said: “Parenting is clearly important, whether children are from a poor or rich background. But poverty is important as well.”

The study of 12,500 British children aged 62 months found the average child from the poorest fifth had a vocabulary age of only 54 months. This compared with 70 for the highest fifth.

The research was carried out by Jane Waldfogel, professor of social work and public affairs at Columbia University and visiting professor at the London School of Economics , and Elizabeth Washbrook of the Centre for Market and Public Organisation at Bristol University.

Baroness Morgan, children's minister, said: “Whilst there is much more to do, the gap between rich and poor in early years is closing ... We will continue to focus extra resources on the most disadvantaged children.”

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