Class size is set to become a key election issue, with almost 80 per cent of parents questioned by market researchers believing that it affects educational achievement.
Parents were not swayed by Government assurances that there is no evidence connecting class sizes with pupil achievement. More than a third of primary pupils - 1,076,173 - were in classes of more than 30 this year.
The survey of more than 13,000 primary school parents will boost Labour's election hopes. The party has made class size one of just five firm policy pledges, promising that under-sevens will not be taught in classes of more than 30. Plastic cards and posters listing the pledges have just been distributed in marginal seats.
The new survey was carried out by ICDmarketing late last year and sponsored by Acorn Computers in association with TheTES. The questionnaire survey of parents of children at 400 primaries, shows that a broad cross-section of parents are worried about class size, including a large proportion of the voters both main parties are anxious to capture.
Party sources said research showed class sizes and standards were a vital issue for parents. Recently-published polls showed that Labour was as much as 30 per cent ahead of the Conservatives on educational standards, while privately-commissioned research is believed to show a 40 per cent lead.
Although Labour has already published its mini-manifesto, the official Conservative line is that the party will not start writing until closer to the election.
Tory sources suggest that after 17 years in power, the manifesto is likely to rely heavily on the party's record on educational reforms with possibly more radical proposals on an issue like selection. There would be no space for smaller, specific policies such as class size.
The party would have more difficulty than Labour in working out where the money would come from to reduce class sizes: Tony Blair's promise, limited though it is, would apparently be paid for by phasing out assisted places, a scheme the Government has just enlarged.
Peter Smith, general secretary of the moderate Association of Teachers and Lecturers which has commissioned its own poll on class sizes, said: "There's a whole credibility gap between what is being said by the Whitehall mandarins, chief inspector Chris Woodhead and Education Secretary Gillian Shephard and what the voter thinks.
"I don't know of a single prep school which doesn't advertise that it teaches groups of less than 30 . . . They market on the basis that teaching groups will be small."
A Harris poll for the ATL last September showed 80 per cent of parents believed large classes threatened education and aggravated discipline problems, 90 per cent demanded a ceiling of 31 on primary classes and one-third preferring a maximum of 20 children.
Of the 13,000 asked about class sizes almost three-quarters own their own homes and around 20 per cent are council tenants.
A third described themselves as housewives, while 10 per cent were professionals, just more than 8 per cent were managers, around 10 per cent were manual workers and just under that number worked in offices or retail.
More than 5 per cent were self-employed, while just under 4 per cent were directors.