Thousands of infant school children in England are in classes of more than 30 pupils - the legal limit.
Pupil numbers are steadily falling
Final statistics from the annual census in January show the number of pupils in Key Stage 1 classes of 31 or more, taught by one teacher, was 20,700.
That was up from 16,400 the previous year, a rise of more than 26%.
But it was several thousand lower than the provisional figure issued in April.
The total number of young children in schools has been falling.
It peaked at 4,140,960 in 1998 and was put at 3,972,690 this year.
The number of primary schools declined over the same period from 18,312 to 17,762.
While the number of support staff in primary schools rose last year, there were 2,780 fewer teachers.
The Conservative Party said the prime minister had boasted at this week's Labour Party conference about how its 1997 election pledges had been met - one of them being to limit infant classes to 30.
"But within days, the government's own statistics show the harsh reality, and reveal that Labour's conference rhetoric is all talk," the Tories said.
A spokesperson for the Department for Education and Skills said: "Overall, average class sizes at both primary and secondary have fallen and this shows we are making real progress but we are in no way complacent and we must work hard to ensure to continue with our key priority to reduce infant class sizes."
Within the totals, the statistics reveal that there were 10 infant classes where between 36 and 40 children were being taught by one teacher.
The most common reason for classes being oversize is that children join the school outside the normal admissions round.
Other reasons include successful appeals for places and pupils' being admitted on the basis of statements of special educational need.
The department said classes could exceed the limit for the remainder of the academic year, after which they must comply with it.