The demand for primary school and nursery places in England will rise dramatically as education budgets cuts begin to bite, new data shows.
The Office for National Statistics says pupil numbers in these areas will rise 8% between 2010 and 2014.
And by 2018 they will reach the highest level for nearly 50 years, according to the projections.
But secondary school numbers are set to fall by almost 5% by 2014, it adds.
A Department for Education spokesman said pupil pressure was a major issue facing the schools system and that tackling it would be a key priority in the autumn's comprehensive spending review.
The ONS figures are published just days after the Chancellor unveiled cuts to the education department of up to 25% over the next four years.
There has been increasing pressure on some local authorities in urban and commuter belt areas, where schools are already struggling to cope with higher pupil numbers.
Extra classrooms have already been built in response, and the former Labour government had to provide extra funding to ease places pressure last year.
In Richmond in south-west London, space for an extra nine classes has had to be added for this autumn, and schools in Surrey have had to accommodate the equivalent of an extra 14 classes of children.
In the London Borough of Lewisham, the equivalent of an extra 17 reception classes will have to be added for the autumn.
The news comes as the ONS also said Britain's population had reached 62m.
Natural population change - births and deaths - currently accounts for more of the increase than migration.
Higher birth rate
The main reason for this is the number of births. In 2008-2009 there were 123,000 more births than in the early part of the last decade.
The school places forecasts are based on population figures for 2008.
They reveal particular pressure on the first years of primary school, with pupils aged five and six alone set to increase by 12% over the same period.
The number of pupils aged seven to 10 is predicted to increase by 6%.
Pupil numbers of those aged up to 15 are expected to be 5% down in 2014 on 2010 figures.
By 2014 all areas of England are predicted to have an increase in their primary age population.
But there are large regional variations with rises of 16% predicted for London, compared to 7% in the south west of England.
Office for National Statistics population figures are also set to be published on Tuesday, based on data from 2009.
The DfE spokesman said the Chancellor had promised to recognise the particular pressures from education in his comprehensive spending review.
"We are bringing in radical plans to increase choice for parents and drive up standards, through expanding academies and freeing up new providers to open schools.
"And we are working very closely with local authorities, particularly in London, to ensure that we meet rising demand for school places effectively over coming years."