Children start their education at a younger age in Britain and have a longer school day than pupils in most developed countries.

Yet Britain is almost bottom of the league table at keeping its teenagers in education beyond the age of 16, with only Mexico, Turkey and Israel doing worse.

It also has among the largest primary class sizes, with almost 25 children per lesson, compared with an international average of 21.5.

Comparatively few young British adults have achieved a basic secondary education, according to the report by the Organisation for Economic Cooperation and Development (OECD).

It found that Britain was 21st out of 29 countries, when it analysed how many 25 to 34-year-olds had five good GCSEs or equivalent. The oldest measured generation (aged 55 to 64) came 13th of 29. South Korea had gone from 23rd to first place.

Andreas Schleicher, of the OECD education directorate, said that Britain had improved but “the world has moved much faster”.

The Labour Government has presided over a huge increase of children aged 3 and 4 in “pre-primary programmes”, from just over half in 1998 to nine out of ten children in 2006, the report, Education at a Glance, says. This compares with an OECD average of seven in ten.

The report found British expenditure on education to be above average, with private sources growing faster than public spending.

Some of that extra money was spent on keeping young primary-age children in school longer than their counterparts. English seven-year-olds endured 100 more hours than average in the classroom each year.

The report said that the UK had among the largest class sizes in primary schools, with only Japan, South Korea and Turkey having more children in lessons. However, class sizes at secondary level were lower than average.

The pace of expansion at university level in OECD countries was outstripping past projections and was expected to continue, it said. While 37 per cent of teenagers in OECD countries went to university in 1995, that figure rose to 57 per cent by 2005.

Britain has an above-average graduation rate, the report said, but had dropped from fourth to 12th since 1995 and was “likely to be surpassed” by other countries. Its dropout rate from degree courses is also relatively high.

Mr Schleicher said that Britain had recently devoted more of its GDP to education than any other country.

It has one of the largest differences in salaries between graduates and non-graduates. Mr Schleicher said:

“In terms of the difference it makes to people’s prospects — those at the high end are having better prospects, those at the lower end are paying a higher price. The spectrum of society is becoming more polarised.”

Anastasia de Waal, of the centre-right think-tank Civitas, said: “The Government must finally commit to a proper class size reduction programme for infant classes.”

The Department for Schools said: “Over the past ten years we have seen steadily smaller class sizes.”

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