Value for money
Increasing class sizes in UK schools could make the education budget stretch further without damaging standards, according to an international analysis of the "efficiency" in education spending.
An efficiency league table puts the UK in 11th place out of 30 countries.
Finland is rated most efficient, in terms of results and spending.
The study highlights that smaller class sizes or teachers' pay are not necessarily linked to better results.
This international study has produced an "efficiency index", which compares how developed countries allocate spending on education and how well they perform in the international Pisa tests.
It focuses on teaching budgets, which researchers say account for 80% of spending on education.
Andreas Schleicher, the OECD's education director, said it "breaks the silence" on the relationship between increased spending and results.
"While spending per student in the industrialised world increased by more than 30% over the last decade, learning outcomes in most countries have remained flat," said Mr Schleicher.
The efficiency index, analysing ?1.34 trillion ($2.2tn) of education spending each year, puts Finland and South Korea in the top places for getting the most value from their school budgets.
Brazil, Indonesia and Switzerland are at the bottom.
The report has been written by Peter Dolton, economics professor at Sussex University, Oscar Marcenaro Gutierrez, associate professor at the University of Malaga, and Adam Still, from education firm GEMS Education Solutions, which commissioned the research.
It raises questions for policymakers about how education spending should be prioritised.
Finland, rated as most efficient, does not have particularly high pay for teachers, but it has very high results.
Underpaying teachers can also be seen as "inefficient" because it is a barrier to recruiting good quality staff - with low pay contributing to Brazil and Indonesia's poor performance in these rankings.
In terms of class size, South Korea is one of the world's highest performers in school tests, but it has relatively big class sizes.
Even though there is often a strong parental instinct to want smaller class sizes, the OECD's research has frequently highlighted that there is no clear link between smaller classes and better results.
The UK, which is examined as a single country rather than four devolved education systems, is among the most efficient in western Europe.
There is the suggestion that there could be more pupils per teacher without damaging results, based on what happens in other countries.
But the report also acknowledges that there are many local cultural factors. Finland might not have the highest pay for teachers, but the profession has a very high social status.
Switzerland has high levels of spending on education and high results. It might also be that "efficiency" is not necessarily the most important objective.
Its high spending might be seen as inefficient compared with other countries, but the outcome could be seen as politically acceptable.
Former Education Minister Lord Adonis said: "There is no easy recipe for a 'good efficient' system. But a highly professional teaching force, which is well but not excessively paid, and with pupil/teacher ratios not excessively small, is a good starting point."
Chris Kirk, chief executive of GEMS Education Solutions, said that this study showed how countries could get better value from their spending.
"At a time at which many countries are struggling with tight public budgets. It also sends an important message to poorer countries that significant educational improvement is possible even with limited investment," he said.
'Value for money' in school spending and results
2. South Korea
3. Czech Republic
6. New Zealand
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