Classroom assistants, rather than teachers, are the answer to large classes, according to the Office for Standards in Education in a report expected to be endorsed by the teachers' pay review body.
The review body, which will publish its own report in January, has been under pressure from the teacher unions to set down limits for class size. The unions buried their differences and submitted joint evidence to the body, which has added weight to their argument.
But the early signs are that the review body is shying away from the politically sensitive issue and will instead suggest using classroom assistants as a solution, on the basis of a survey it has carried out .
Today a report by OFSTED, based on 20,000 school visits, will say that class size is linked to pupil achievement only in the first two years of primary education. While children need more individual attention when they are learning to master basic literacy and numeracy, once they have these skills then class size has no bearing on their exam results.
The OFSTED evidence is certain to be seized on by ministers to counter protests from parents about rising class sizes because of cuts.
Earlier this week Chris Woodhead, the chief inspector, claimed there are 15,000 incompetent teachers in the state system and that they deserve to be sacked. This would work out as two teachers per secondary school and one incompetent teacher for every three primary schools.
However, the figures also show there are more than three times as many excellent teachers. According to OFSTED there are an estimated 48,000 staff teaching lessons graded at 1 - the top mark.
But this in turn reveals an alarming disparity between the primary and secondary sectors, with each secondary school boasting an average of eight excellent teachers in comparison with less than one top teacher per primary. Secondary schools have 30,000 staff teaching grade 1 lessons; primary schools only 18,000.
A third of primary-school children are now taught in classes of 30 and more.
Doug McAvoy, general secretary of the National Union of Teachers, disputed the OFSTED findings on class size and the level of incompetence in the profession. He said: "If a teacher is in difficulties, they should receive extra training and if that support has been provided, teachers who are still ineffective should be asked to leave," he said.