Rishi Sunak leaves 10 Downing Street to attend prime minister's questions.
The prime minister said giving them charitable status - which means they don’t have to pay VAT - was “about supporting aspiration”.
His comments came during angry clashes with Labour leader Keir Starmer at prime minister’s questions.
Labour has pledged to scrap the tax perks for private schools if the party wins the next election, with the money raised spending on improving state education.
Having charitable status saves the private school sector around £1.5bn in VAT and £150 million in business rates.
At PMQs, Starmer took aim at the prime minister’s old private school and asked why it receives “taxpayers’ money”.
He also pointed out that levelling up secretary Michael Gove has previously called for private schools to lose their charitable status.
“Winchester College has a rowing club, a rifle club, an extensive art collection, they charge over £45,000 a year in fees,” the Labour leader said.
“Why did he hand them nearly £6 million of taxpayers’ money this year in what his levelling up secretary calls ‘egregious state support’?”
Sunak said the government had recently announced “billions more funding for our schools”.
He added: “Whenever he attacks me about where I went to school, he is attacking the hard-working aspiration of millions of people in this country, he’s attacking people like my parents.
“This is a country that believes in opportunity not resentment. He doesn’t understand that and that’s why he’s not fit to lead.”
But Starmer said: “He talks about his record. It is simple, he can carry on being pushed around by the lobbyists, giving away £1.7 billion to private schools every year or we can put that money to good use. End the Tory scandal.
“He talks about his record. Hundreds of thousands of children leaving school without the qualifications that they need. I have made my choice, what is his?”
Sunak said the government was “improving school standards for every pupil in this country”.
He added: “This is about supporting aspiration, and that is what this government is proud to do.”