Politicians the world over leave no stone unturned in their quest to raise their nation's ranking in the all-important Pisa (Programme for International Student Assessment) league tables. The length of the school day and the number of weeks in the school year have now come to their attention and are being trawled through for any sign that they might force up results.
US president Barack Obama recently stated: "Our children spend over a month less in school than children in South Korea every year. That's no way to prepare them for a 21st-century economy."
And Michael Gove, England's education secretary, recently praised the educational performance of East Asian nations and attributed their success to working longer and harder. He argued that if students in England are to reach the achievements of their East Asian counterparts, "a higher level of effort is expected on behalf of students, parents and teachers. School days are longer, school holidays are shorter."
Let's be honest, teachers around the globe, already exhausted by the endless demands of the job, would welcome longer working hours and longer weeks like a hole in the head. The profession has a right to know, therefore, whether there is good evidence that more hours of teaching would result in better attainment.
Let's take two examples of very different approaches to schooling. According to the Pisa league tables, South Korea and Finland both have top-performing education systems, and yet their school years and daily timetables could not be more different. South Koreans attend school 220 days a year. Finnish students see less of the classroom: their school year is 188 days. (Students in the UK attend schools on 190 days, those in the US on 180 days.)
The school day in South Korea is unusually long, beginning at 8am and finishing at 4.30pm. Finnish students spend fewer hours in school. Their school day lasts between four and seven hours and, with only half an hour's homework, they have plenty of time away from school and school work to develop their own interests and direct their own activities. For many South Korean students, however, the end of the school day is not the end of formal study because there is a thriving business in fee-paying, late-night tutoring, where parents pay for extra tuition to give their child the edge in highly competitive national exams. As has been written elsewhere, shockingly, South Korean children can spend 13 hours a day studying.
If there were a simple equation between time spent in formal schooling and academic success, South Korea would retain its top Pisa ranking and Finland would plummet down the league tables. The fact that Finland stays at the top of the tables means that there must be other explanations for its success. And there is another problem for the work-longer, learn-more school of thinking because Finland is also top of the table in "study effectiveness", the correlation between the hours of study and standards achieved. South Korea fares badly on this measurement - 24th out of 30 developed nations.
So, if it is not time tied to the school desk that is behind Finland's excellent study effectiveness, what could be the explanation for its success? The possible reasons are likely to be less attractive to the politicians. They would include the fact that Finland is a much more equal society with less wealth inequality than the US and the UK. Extensive research shows that childhood poverty blights children's development, their mental and physical health, and that the effects continue throughout adulthood. There is no getting away from a simple truth: the long tail of educational underachievement in the US and UK is directly linked to the large number of children in those countries living in poverty.
When it comes to education, Finland challenges the educational orthodoxy of the US and the UK. Finnish children don't start school until they are 7. There are no private schools. Indeed, it is illegal to charge school fees in Finland. The vast majority of Finnish students go to their local comprehensive school, where they are taught in mixed-ability classes. There is little or no competition between schools, and very little variation in the standards achieved between them.
The teaching profession in Finland is very different from that in the UK or US. All teachers have five years' initial training, which leads to a master's qualification. Teaching is one of the most highly prized professions, on a par with medicine and the law. The Finnish national curriculum is also light touch, giving teachers great discretion in what they teach.
Given politicians' professed belief in evidence-based policy, it might be thought that each one of these factors would be the subject of serious and sustained political analysis. The fact that they have lighted upon the chimera of hours and weeks spent in the classroom says more about the limits of their political thinking than anything else. Their nations' children, and teachers, deserve more.
Dr Mary Bousted is general secretary of UK teaching union the Association of Teachers and Lecturers.