More primary schools in Wales have broken the Assembly government's class-size limit this year than last, and some are being told they only have until next month to meet the 30-pupil maximum. But Jane Hutt, education minister, maintained last week that the latest class-size figures were "excellent".
Statistics for September show 68 infant classes had more than 30 pupils, compared with 51 last year. This amounts to 2.3 per cent of pupils being taught in overcrowded classrooms, compared with 1.7 per cent in 2007.
Although just 15 of the 3,991 infant classes in Wales had more than 30 pupils after legally permitted exceptions, Ms Hutt has warned schools to fall in line. "I will expect everyone concerned to make every effort to prevent future rises in class sizes," she said.
The Assembly government was unable to account for this year's class-size hikes. A spokeswoman said: "It would be unwise to speculate on reasons for any increase in numbers, particularly as these are very small. The results of the class size count are carefully monitored and action (will be) taken."
Infant classes have been subject to the 30-pupil maximum since 2001, but the limit has met with mixed views from teachers. While many see the benefit of smaller classes, some feel it is too inflexible.
"Children aren't born in convenient numbers," said Iwan Guy, of heads' union NAHT Cymru. "I've seen instances where a teacher would rather have 32 in one class than see two taught separately."
Elaine Edwards, general secretary of UCAC, the Welsh medium teachers' union, said: "We've had a few examples where people have juggled sizes by registering pupils in one class and moving them into another group to teach.
"At one large town primary I know, the numbers mean it should have a three-class intake. But it can't afford the staff and hasn't got room, so it will have to have two."
The latest figures show breaches of the 30-pupil limit are also up on last year in junior classes - 194 classes compared with 162 in 2007.
Of the cohort, 194,120 had permissible exceptions.