More than 40,000 children in the North-East are being taught in classes of more than 30, Government figures yesterday revealed.
A total of 43,209 children are being taught in large classes in the region, despite evidence that children do better in smaller groups.
Of those, more than 4,500 are in classes of more than 36 children, while almost 1,500 infant schoolchildren are being taught in classes of more than 30, even though this has been against the law since 2001.
Parental groups last night hit out at the figures and said that children were being harmed by being taught in large classes.
Teaching unions also criticised the situation and called on the Government to put a halt to staff cuts in the region.
But the Government said that average class sizes in the North-East were coming down as teacher numbers reached record levels.
David Butler, chief executive of the National Confederation of Parent Teacher Associations, said: "Parents will be concerned that class sizes are higher than 30 - the current legal maximum for Key Stage One children. Smaller class sizes benefit children, allow the teacher more time with each child and improve the child's achievement."
Mick Lyons, North-East national executive member for the teaching union NASUWT, said: "This is a product of the stupid system where funding for schools follows bums on seats."
In County Durham, more than 6,000 primary school children - around one in five - were taught in classes of more than 30 last year. Northumberland had the highest figures for secondary pupils in large classes, with 4,500 (20%) pupils in that situation. Since September 2001, all infant classes have been required by law to contain 30 pupils or fewer, except in very limited circumstances and for limited periods of time.
But the Government figures showed that there were 40 infant classes in the North-East over the limit last year.
Schools Minister Jim Knight said the Government had made "significant progress" to limiting class sizes in infant schools.
But he said: "There has been a small rise in the number of infant classes - with valid exceptions - where numbers exceed 30 children. We have a range of legal powers that can be used to ensure that schools fulfil their legal obligations on class sizes and there should be no doubt that we will not hesitate to use them where necessary."