Jeremy Corbyn accused Theresa May of pursuing an education policy of "segregation" as the pair clashed at Prime Ministers Questions over the Government's aim to introduce new grammar schools.
The Labour leader dedicated a series of questions to the controversial policy, challenging the Prime Minister to name any education experts that back her on introducing more selection into schools.
Mrs May refused to name a significant backer, but accused Mr Corbyn of living in the past, saying: "Can I say to the honorable gentleman that he needs to stop casting his mind back to the 1950s."
Despite opposition from some sections of her own party - including the outgoing former prime minister David Cameron - on selection, she attempted to define the difference between her party and her rival leader.
"He believes in equality of outcome. We believe in equality of opportunity," she said. "He believes in levelling down. We believe in levelling up."
Mr Corbyn replied: "Equality of opportunity is not segregation at the age of 11."
Mrs May said both leaders had benefitted from the system. "He went to a grammar school. I went to a grammar school. It's what got us where we are today."
Mr Corbyn said he wanted the education system to offer "good education for every child".