The NUT wants primary school classes limited to 26 pupils

The National Union of Teachers voted to launch a major advertising drive and a petition aiming to attract one million signatures to protest over the issue.

Delegates at its annual conference demanded that classes be limited to a maximum of 26 pupils.

The Department for Education said primary school class sizes had fallen since 1997.

Sasha Elliot, from Camden, called for a campaign "with a similar spirit" to that which Jamie Oliver showed when he brought the issue of school food to the top of the agenda.

She said: "Old Jamie, if he showed us one thing, it was that where education is concerned, successful, nationwide campaigns that focus on straightforward common-sense truths motivate all sorts of people to activism."

She added: "Reducing class sizes is not a panacea for all the ills in education, but it is certainly a move that will impact positively on almost all aspects of teaching and learning."

Motion

Delegates backed the motion, which urged other teachers' unions to join the campaign, along with MPs, parents and school governors.

The government changed the law to limit class sizes to 30 for five to seven-year-olds.

But the NUT motion condemned the "waste" of government funding on controversial initiatives such as the city academies programme, arguing that the money would have been better spent on cutting class sizes further.

The Department for Education and Skills said primary school class sizes have fallen since 1997 and remained the same in secondary schools.

A spokesman said: "We now have record levels of teachers - 431,900 full time teachers up from 399,200 in 1997, and support staff and standards have never been higher .

"We are going further still by supporting teachers in meeting the individual needs of every child. By 2007- 08 schools will receive �930m to support those falling behind, stretch the brightest, deliver small group teaching and provide intensive one-to-one support."