David Cameron insisted he was showing "leadership" by defying criticism from Tory grassroots over his grammar school policy.
Focusing on pushing up standards across education is vital and far more "aspirational" than attempting to expand the selective state system, Mr Cameron said.
But he denied he was trying to "pick a fight" with his party's right wing - who have long viewed grammar schools as an article of faith - or emulate Tony Blair's 1995 "Clause Four" moment when he faced down Labour traditionalists over the commitment to nationalisation.
Asked on BBC Radio 4's Today programme why he was defying the outcry among activists and MPs with his education stance, Mr Cameron said: "I lead. I don't follow my party. I lead them.
"This is the direction which we must go to deliver the aspiration, the opportunity and the social mobility that all of us Conservatives feel passionate about."
The previous Tory government had not managed to expand the grammar school system significantly during the 18 years it was in power, and it was clear that parents did not want to see their children subjected to selection aged 11, he insisted.
Mr Cameron said the key was to drive up standards across the board and have "parents choosing schools and not schools choosing parents".
He stressed that no existing grammar schools would be forced to close under the policy, and dismissed the furore as a "pointless debate".
Mr Cameron said: "I'm not turning it into a Clause 4. I feel very passionately that I want the party to make the real steps necessary to deliver opportunity for all.
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"The debate about a few more grammar schools has stopped us from doing that, because it's a policy we didn't introduce, we wouldn't introduce, that wouldn't be sustainable even if we did, and isn't anyway the right thing to do."
