Angry head teachers heckled Education Secretary Justine Greening as she told a conference about her plans for new grammar schools.
There were cries of “rubbish” and “no, no” as she said selective schools could close the achievement gap between rich and poor pupils.
And the head of Ofsted said too many schools boosted results by removing pupils not expected to do well.
Amanda Spielman called the tactics “nothing short of a scandal”.
Ms Spielman, who took over as chief inspector earlier this year, told delegates: “Childhood isn’t deferrable: young people get one opportunity to learn in school and we owe it to them to make sure they all get an education that is broad, rich and deep.”
And speaking later on BBC Radio Four’s World at One, she described a “corrosive” culture in some schools where league table success took precedence over other aspects of education.
The Association of School and College Leaders annual conference is taking place in Birmingham this weekend, against a backdrop of increasing frustration among head teachers about budget cuts.
Ms Greening’s speech came days after money was pledged in the Budget for new grammars and free schools – but there have been complaints that schools’ demands for help with their running costs were not answered.
ASCL has a reputation as one of the more moderate education unions, but interim leader Malcolm Trobe, told journalists that some schools were looking at closing early a couple of times a week in order to make the sums add up.
“A number of people are thinking about reducing the number of lessons in a week – maybe having a shorter Wednesday and a shorter Friday,” he said.
“There’s a huge amount of anger out there about the amount of cuts we are having to make,” he added.
“The majority of the funding pressures are government imposed – teacher pensions and National Insurance.
“We know that money is needed for new schools but then to say something about making them selective will really have wound people up.”
Ms Greening was given a polite welcome by delegates when she began her speech, but some delegates began to murmur when she began answering a question about grammar schools.
She said: “We have to recognise that actually for grammars in terms of disadvantaged children they really do help them close the attainment gap.”
She added that parents were also keen as the schools were over-subscribed.
This prompted cries of ”rubbish” and ”shame” from dozens of delegates.
The National Audit Office reported that schools needed to find £3bn savings by 2020.
Ms Greening told heads she was listening and she did not wish to “minimise” the pressures faced by schools.
She suggested the Department for Education may be able to offer targeted support for schools in the most challenging circumstances, but it was not clear what form this support would take.
Education secretary heckled by angry head teachers}