More than 1.26 million pupils, almost a third of all primary schoolchildren in the country, are now being taught in classes larger than 30, an increase of 9 per cent on last year.
The number of pupils in classes with more than 35 children has also risen by 63.5 per cent to 130,000 in the past four years, according to the 1996 provisional figures produced by the Department for Education and Employment.
The average primary class currently has 27.3 children, compared with 25. 4 eight years ago.
A spokesman for the department said that there are now far fewer small classes, which had kept the average number down in the past.
Class sizes in secondary schools have risen from 20.6 to 21.6 over the past 10 years.