The countdown has begun. In early December, governments around the world will be able to find out how well 15-year-olds are doing in their schools.

If the last two sets of PISA (Programme for International Student Assessment) results are anything to go by, the firm favourite to top the international table will be Finland. The Nordic country was judged to have the most able pupils in the developed world in 2004, and again when the most recent results were published in 2007.

Such public displays of educational excellence have made Finland the envy of other OECD countries. But its increased profile has also led to problems for the country of just 5.5 million people.

Helsinki’s 140 schools are now inundated with officials and teachers wanting to discover the secrets of their success, visitors that one Finnish newspaper has dubbed “PISA tourists”.

Eva Pentilla, head of international affairs in the Helsinki Education Department, says she now rejects all applications from foreign teachers as a matter of policy. “In Helsinki itself, we now only accept high-level guests such as presidents, government ministers, officials and high-level researchers,” she said.

“Principals, teachers and students are encouraged to contact other cities in the region, such as Espoo or Vantaa, or other cities in Finland.

Rejection by Helsinki’s Education Department does not seem to have deterred eager educationalists from their quest to witness Finnish schooling first-hand. Oulu, a city of 140,000 almost 400 miles north of Helsinki, is also having to turn away foreign teachers, because of the sheer numbers wanting to visit.

The city now offers job-shadowing for foreign teachers, which is funded by the EU, to give a more in-depth look at what is happening in the classroom.

But Mrs Pentilla, a former president of the European School Heads Association, warns that visits are pointless if the culture of a country is radically different from that in Finland.

“It is my responsibility to try to make trips worthwhile,” she said. “But even I sometimes think: `Come on, our societies are so different!’”

In a few weeks, Finland will find out if it has continued its table- topping performance. If so, expect Mrs Pentilla’s warning to fall on deaf ears as foreign educators continue to hunt for the secrets of the country’s educational success.