The coalition's flagship Pupil Premium will see schools get an extra £430 for every poorer child on their books next year.
The Liberal Democrat-inspired supplement is slightly lower than some had expected, the Government pumping in 625m for around 1.4 million less well-off young people in 2011-12.
However, it is due to rise significantly by 2014-15, when spending will reach 2.5bn.
Deputy Prime Minister Nick Clegg said handing over the premium for every child who receives free school meals would have more benefit for social mobility than keeping tuition fees down.
"When money is tight, you have to be really clear about what your priorities are," Mr Clegg said. "One of mine has always been making sure that the most disadvantaged children in this country get the help they need.
"Despite the recent controversy, all the evidence shows that the best way to help bright kids from poor families get to university is to target additional resources at them when they are younger and so give them a head start in life.
"By targeting money directly at our poorest children, the coalition Government is starting on the long and hard road to breaking down one of the most socially segregated education systems in the developed world."
As the cash allocated to the policy increases in future years, the amount per child will rise and more pupils will be covered. Funds will also be weighted to areas of the country where they are most needed.
Schools will have freedom to choose exactly how the extra money should be used.
Education Secretary Michael Gove will confirm details of the premium when he announces the schools settlement today.
Treasury Chief Secretary Danny Alexander accepted that some of the money for the pupil premium would come from within the existing schools budget.
"We have been able to ensure that the schools budget rises in real terms," he said.
"That is what the settlement does. By doing things like freezing the pay of public sector workers, including teachers, we are giving more spending power to schools but we are seeking to focus rises within that on the most disadvantaged children."
Pressed on whether the pupil premium means some schools would receive extra funding at the expense of others, Mr Alexander said: "It is included within the overall settlement, but the schools budget, the cash amount per pupil is going to stay the same."
Labour Shadow Business Secretary John Denham criticised the arrangements and said: "It's a con, that's the trouble.
"If it was new money going to the poorest pupils, I'm sure we would be very pleased about it.
"This is money that's already in the education budget, simply being redistributed, robbing Peter to pay Paul.
"About two thirds of schools are going to see shrinking budgets – so this isn't any sort of victory for the Liberal Democrats."