Statutory limit of 30 infants in one-teacher classrooms breached in nearly 3,000 cases, finds annual census.
One in eight pupils in primary schools in England are being taught in classes that are bigger than the government's statutory maximum size, official figures published have revealed.
The annual school census shows that 12.5% of primary school pupils attend classes which have more than 30 children. There are more than four million primary school pupils in the UK.
The steady rise in classroom overcrowding in recent years is attributed mainly to the rising birth rate.
Russell Hobby, general secretary of the National Association of Head Teachers, said: "The rise in the number of primary age pupils has been known about for a long time. The government has simply not done enough to look at where those school places are going to be needed and to provide the resources and spaces for them." He said that schools were prevented from planning ahead "by a fragmented system".
The London borough of Harrow is rated the worst off for overcrowding. While the average size of a primary school class is 27.4 pupils, a slight increase from 2013, Harrow has an average of 30.2 pupils for each class. A fifth of all the above-maximum classes are in London.
The statistics gathered from all of England's schools show that nearly 30% of pupils at primaries and a quarter of pupils at secondary schools are from ethnic minority family backgrounds, with 60% of the increase in primary pupil numbers attributed to ethnic minority pupils.
There has also been a slight increase in the number of pupils for whom English is not their first language: 654,000 pupils at primary schools, compared with 612,000 last year.
In total about 1.12 million pupils in state schools do not speak English as their first language, compared with 1.07 million in 2013.
The survey, conducted this January, shows a 2.5% increase in pupils attending state-funded primary schools in the space of a year. Primary pupil numbers have been rising each year since 2009, reversing the trend that occurred between 2003 and 2009 when primary pupil numbers declined in line with the falling birthrate at the time.
In 2014, nearly 3,000 infant classes, at Key Stage 1, breached the statutory ceiling of 30 pupils in one-teacher classrooms, with more than 2,400 doing so legally and a further 500 more classed as having unlawfully broken the numbers limit.
Schools are allowed to have classes of more than 30 in certain circumstances, such as where an admissions appeal is upheld or when there are late admissions with no alternative school available.
The rapid increase can be seen in the number of children in oversized classes serving infants, including reception classes. About 94,000 are being taught in classes of more than 30, compared with just 31,000 in 2010, while the average class size has jumped to 27 owing to 200,000 extra children enrolled during the same period.
A Department for Education spokesperson said: "The average infant class size is up only marginally, from 27.3 to 27.4. However we recognise the significant pressure on school places as a result of demographic trends over the last decade.
"That is why we are giving local authorities £5bn to spend on new school places over this parliament – double the amount allocated by the previous government over an equivalent period.
"This funding has already led to the creation of 260,000 new school places, all of which are in areas where there is a shortage of places, and many more new places are planned."
Labour blamed the rise on the coalition. Tristram Hunt, the shadow education secretary, said: "David Cameron and Michael Gove promised small schools with smaller class sizes. Yet in government their decisions have meant thousands more children are being crammed into overcrowded classes, threatening school standards.
"They have created a crisis in school places, spending hundreds of millions of pounds on free schools in areas that already have enough schools places, and children are paying the price."
Labour also pointed out that the number of "titan" primary schools had risen: 77 primary schools now had more than 800 pupils, compared with just 16 in 2010.
Outer London was revealed as the region where primary schools were most under pressure with regard to infant class places, with an average of 28.8 children in one-teacher classes. The smallest classes were in Cumbria, with just 23.5 pupils per class.
The school census also showed that there are more than 2.4 million pupils being taught in 3,827 academies and free schools. Almost 30% of all school pupils in England are enrolled in academies and free schools.
There was also a slight dip in the proportion of pupils receiving free school meals. Last year 17.1% of pupils claimed free school meals, but 16.3% did so, the following year, in 2014.
