A return to a grammar school education system would deepen the divisions between rich and poor, the Conservatives say.
Shadow Education Secretary David Willetts rejected the view - for years a strongly held Tory belief - that academic selection is the best way to raise school standards.
And he claimed that the Tories would build more of Tony Blair's favoured privately sponsored city academies than will be opened under a Gordon Brown government.
In a speech to the CBI, Mr Willetts said: "We must break free from the belief that academic selection is any longer the way to transform the life chances of bright poor kids. This is a widespread belief but we just have to recognise that there is overwhelming evidence that such academic selection entrenches advantage, it does not spread it."
He continued: "A Conservative agenda for education will not be about just helping a minority of pupils escape a bad education. We want better schools for all, based on fair admission and fair funding. That is why we are outlining a series of specific measures for driving up standards and expanding the academies programme begun by Tony Blair."
Left wing Labour MPs and teachers' unions had hoped that Mr Brown would abandon the academies initiative, which they have branded the "privatisation" of state education.
On Tuesday, the Chancellor gave his backing to the city academy scheme, telling the BBC it was "right" that wealthy individuals "put something back into the community".
At the same time, Education Secretary Alan Johnson said the Government would "limit" the number of academies to 400.
Mr Willetts backed academies and promised to open more. He said Mr Blair's academy model of privately sponsored independent state schools was "a powerful route to higher standards".
"And as part of his legacy he now leaves behind him legislation which we can use to push his academies much further forward than Gordon Brown would ever dare to do," he said.
