The Education Secretary Justine Greening was jeered at and heckled by head teachers as she suggests that grammar schools can raise attainment in disadvantaged children.
Members of the Association of School and College Leaders (ASCL) shouted "rubbish" at Ms Greening as she spoke in support of the Government's plans to set up more grammar schools.
This week Prime Minister Theresa May unveiled plans for building a generation of new grammars, with £320 million set aside in the Budget to help end what she called the “brutal and unacceptable” truth of selection by income.
On Friday, Ms Greening was forced to defend the policy as she faced a hostile audience of secondary school head teachers.
We should recognise that parents also want choice for their children and that those schools are often very over-subscribed
What Justine Greening said as she was being heckled
Asked by a headteacher from Devon why Government policy "flies in the face" of evidence on grammars' impact on social mobility.
Ms Greening, who was giving her keynote speech at the ASCL annual conference in Birmingham, was laughed and shouted at as she insisted that grammars "really do help them close the attainment gap".
She told delegates: "First of all, in terms of grammars but also the investment that we announced for more schools beyond 2020, I think it is important that we're planning ahead.
"We know we've got a demographic bulge that's already been in our primary system and that really is flowing into the secondary system as well.
"So we need to have an eye on that and, of course, as a Government we've had brought forward the Schools that Work for Everyone consultation to really say 'What is it going to take to really drive social mobility?'."
Dozens of ASCL members jeered as the Education Secretary added: "We have to recognise that actually for grammars in terms of the disadvantaged children that they have, they really do help them close the attainment gap.
"And at the same time we should recognise that parents also want choice for their children and that those schools are often very over-subscribed."
Ms Greening went on: "I think we have to respond to that and the consultation wasn't really just about selection it was also about how other parts of the eduction system can also play a role in strengthening our overall school system, whether it was selection, whether it was universities or indeed independent schools and faith schools.
"So we want to make sure that we take on board all of the comments. But we also will come forward with what I hope will be a very strong package that doesn't just look at how selection has performed in the past, but very much looks forward to what a sensible approach on selection - which we do have in our system - should be in the future."
The ASCL, whose members include some grammar school head teachers, has warned the Government against creating more selective schools.
In a speech to the conference, ASCL interim general secretary Malcolm Trobe said: "There is no evidence to support the Prime Minister's current conviction that doing so will improve standards and social mobility.
"Our members leading grammar schools do a fine job with the young people in their schools but although the creation of more selective schools may improve social mobility for a very small number of disadvantaged children, it will not for the vast majority.
"We need solutions which help the many, not just the few. We need as many people as possible to have the high-order knowledge and skills that will enable us, as a nation, to compete on a world stage."
Prime Minister Theresa May has argued that grammars can help the life chances of poor pupils and that the current system sees ''selection by stealth'' based on parents' wealth and ability to buy houses near the best schools.