Reducing class sizes is not the most efficient way to raise school standards, the world's governments were advised this week. And the message - this time coming from the Organisation for Economic Cooperation and Development (OECD) - may be getting through.
The body's annual Education at a Glance report reveals that primary classes (typically for children aged 4-11) in most of its member countries have remained relatively static over the past decade. But it also reveals that the UK is one of only two countries studied where lower secondary classes (typically for children aged 11-14) are smaller than those of primary students.
According to OECD education special adviser Andreas Schleicher, that is the wrong way round.
"You (the UK) have the smaller classes later in a student's life where probably the (beneficial) influence is less pronounced," he said. "From our perspective, we haven't seen any impact of declining class sizes. But I think if you do decrease class sizes then it matters more in the early years. In lower secondary and upper secondary you can afford to have larger classes."
In the UK, the average size of a lower secondary class is 19.5 students, much smaller than the average of 25 for all primary classes, according to the OECD report, which looked at class sizes in 30 countries. The only other country where the smallest classes are in secondaries is Estonia. But here the difference is far smaller: 17.4 students compared with 16.7 in primaries.
While the main message from the OECD was that size does not matter that much anyway, this did not prevent negative headlines in England last week. Department for Education figures showed that the average class size for infants aged 4-7 had risen marginally, from 27.2 to 27.3 since 2012, and the number of infants in classes of more than 30 had more than doubled, from 28,875 in 2009 to 71,935.
The issue is being compounded by a shortage of school places, with the National Audit Office warning that an extra 256,000 will be needed in England by September 2014.
The OECD report shows that some countries have experienced significant falls in class sizes in the past decade. This has happened most notably in South Korea, where primary classes plummeted from an average 36.5 in 2000 to 26.3 in 2011.
Mr Schleicher said the fall could be explained by demography: "They have fewer young people."
"Of course a smaller class is always better than a larger one," he added. "But if you have an extra pound to spend, do you spend it on a better teacher or more instruction hours, or on more non-teaching working time or more professional training?
"And when you put all these things together, decreasing class size is not actually a great way to raise efficiency."
A spokesman for England's Department for Education said: "Children are only permitted to join primary classes of 30 pupils in exceptional cases ... Classes often fall back naturally to 30."
Average class sizes in primary education, 2011
38 - China
30.4 - Chile
24.8 - UK
23.5 - Australia
22.7 - France
21.2 - Germany
20 - US
15.7 - Luxembourg