By Hannah Goff
BBC News at the NUT conference, Manchester
Teachers may strike over the issue of class size
Pupils are being taught in class sizes of up to 55 in some parts of the country, teachers have claimed.
Delegates at the annual NUT conference in Manchester said excessive class sizes were a "national scandal" and entrenched social inequality.
The union is calling for a maximum class size of 20 by 2020 and is threatening rolling industrial action.
The UK comes 23rd in a league table of 30 developed countries' class sizes, with a primary school average of 25.8.
A teacher from St Helens, Robin Pye, said smaller class sizes would do a great deal for the life chances of young people.
He said 40% of primary schools in his area had class sizes in the mid to upper 30s, despite rules limiting them to 30.
Mr Pye described how one teaching colleague took a class combining three year groups and three pupils with special educational needs, with no help from a teaching assistant.
Birmingham teacher Stuart Richardson compared the situation in the state sector with a private school where a teacher friend had groups of two, five and nine pupils.
He argued that excessive class sizes entrenched social divisions, and argued for an end to all school closures prompted by the fall in pupil numbers in secondary schools.
Delegates also debated the burden teachers face in their working lives, which might also be the subject of future industrial action.
Andrew Stone from East London said teachers were "driven to distraction" by unmarked books and "box-ticking lesson plans".
He said teachers wanted schools to be places where the "rose-tinted recruitment ads" bore some relevance to reality.
Tom Woodcock from Cambridgeshire said teachers were struggling against a culture of form-filling and excessive monitoring.
"Teachers are angry, they are beyond angry, and many have voted in this debate already, many have voted with their feet," he said.