Conservative leader David Cameron has warned that the row over grammar schools was a "key test" of whether the party was fit for government.
He said the issue would show whether the Tories were now "an aspiring party of government" or whether they were to be a "right-wing debating society".
Critics were "splashing around in the shallow end of the educational debate".
There has been anger in the party at the dropping of the idea that selective schools could help social mobility.
Writing on the Conservative Party website, Mr Cameron also accused critics of "clinging on to outdated mantras that bear no relation to the reality of life".
'I lead, not follow'
Instead of grammar schools and selection by academic ability, Mr Cameron has promised more city academies - the privately sponsored state schools championed by Prime Minister Tony Blair - and more streaming and setting within schools.
The Conservative leader's comments come amid unhappiness from some Tory MPs and supporters over the end of support for academic selection.
Mr Cameron told BBC Radio 4's Today programme: "I lead. I don't follow my party; I lead them."
He added that the Conservatives had not expanded grammar schools while in power from 1979 to 1997.
"At the heart of this is the oldest British obsession of them all - class"
Selective education was "unpopular with parents. They don't want children divided into successes and failures at 11."
Mr Cameron also said: "I'm determined to do what's right for my party and the country."
There are 164 grammar schools in England - choosing pupils by academic ability at the age of 11 - with 10 local education authorities considered to be fully selective.
Mr Cameron said last year that there would be "no return" to the 11-plus exam or more new grammars.
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Conservative education spokesman David Willetts went further last week however when he said that selection by ability at age 11 did not work, or help social mobility.
He said this was because middle class parents could coach a less bright child to do better at age 11 than a bright child from a less well-off background.
There are no plans to change the status of any of the existing grammar schools.
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