Education is everything, says Nick Clegg
The Liberal Democrats would tie extra cash to England's deprived pupils so they can get a "fair start" at school.
The current outcome for poor children was "horribly unfair", said the party's leader, Nick Clegg,
He pledged to transform school funding with a £2.5bn "pupil premium" in which extra cash would follow poor pupils.
This would mean an extra £2,500 for each child on free school meals, he said, but insisted it would benefit all school children.
In a speech setting out his party's policies on education and inequality, he said: "By age seven a bright but poor child will have been overtaken by his or her better off classmates.
"By age 16 poorer teenagers are only half as likely to get 5 good GCSEs as everyone else."
He acknowledged that the Labour government had put more money into the education system, but it had failed poor children, particularly those from the inner cities, he said.
He said: "It hasn't done anywhere near enough to reach out to children from all disadvantaged backgrounds and give them the leg-up they need."
Lib Dem research showed there was a huge variation in the performance of poor pupils living in different parts of the country, he added.
The pupil premium, the party's largest spending commitment, could lead to an average of £2,500 for every child on free school meals, he said.
More catch-up help
It works by targeting extra funds at schools which take on children who need more help.
It would top up the existing basic per pupil funding and would follow a pupil if they switched schools.
An average primary school of 200 pupils, with an average number of children on free school meals, would have an extra £90,000 in its budget.
This could reduce class size from 27 to 20, ensuring that every child would get the attention they need.
In an average secondary school, with 1,000 pupils it could mean an extra £400,000 every year. This could be used to recruit 12 extra teachers and cut class sizes to 16, or it could be used to pay for catch-up help for 160 pupils.
Currently schools in England get extra money for deprivation levels on top of the per pupil funding. But this is based on average local authority free school meals levels.
They also get different pots of money for a range of different pupil characteristics such as English as an additional language.
The Lib Dems say that one in three pupils on free school meals attend schools in relatively affluent areas and so miss out on funding.