Clare Dean reports as the education authorities lobby the Secretary of State.
It's official - and even comes from the highest of sources: large classes in schools cause problems.
Gillian Shephard has publicly admitted for the first time that difficulties are created by large classes. Difficulties for the teacher in terms of crowd control, that is, if not necessarily for the child attempting to learn.
"We all know that it is much more difficult to teach a large class," the Education and Employment Secretary told the Council for Local Education Authorities, meeting in Brighton last week.
Before education directors and councillors could celebrate her acknowledgement, Mrs Shephard quickly added: "But all headteachers know that class size is not simply a function of funding."
With more than a third of primary pupils estimated to be in classes of more than 30 from September, and with ministers ever ready to insist that large classes have no effect on a child's ability to learn, Mrs Shephard is under pressure to prove the strength of the Government's argument.
The 116-member CLEA, which represents both the shire counties and the metropolitan authorities, is demanding that she institutes a detailed investigation into the effects of class size on pupil performance.
Professor Peter Mortimore from the Institute of Education at the University of London has already submitted a research proposal to the Department for Education and Employment.
He told the CLEA that evidence on small classes from the United States showed that there was a slight benefit for young children - but at a high cost.
And he urged LEAs and heads to keep reception and Year 1 classes smaller than the rest.
But he warned: "Reducing class size by itself isn't enough - there must be in-service training and extra coaching - but where it does work is that teachers are more enthusiastic about smaller classes and that is carried over to pupils."
Delegates called on the Government to recommend maximum pupil:teacher ratios for each key stage and to emphasis the figures in the Parent's Charter.
And Sir Geoffrey Holland, vice-chancellor of Exeter University and former permanent secretary at the Department for Education, warned that Britain's education system was now failing children at a rate so alarming that it would bankrupt any company.
He said pupils and parents should be entitled to compensation - either cash or in the form of extra help at school - if they believed they had been let down.