The UK is above average in a major international league table on school science - but it has slipped compared to its previous top-four ranking.
Only half of students in England said they found science fun
Finland, Hong Kong and Canada were the top-rated countries for science.
The study of science ability among 15-year-olds in 57 countries ranked the UK between 12th and 18th place.
In 2000, the UK was in fourth place, but the organisers warn that comparing results in this three-yearly assessment is not "strictly valid".
When compared only with other members of the OECD in the Programme for International Student Assessment (Pisa) study, the UK came between 8th and 12th place - using a system which places countries within a range of rankings.
This places the UK's teenagers in a top group defined as "statistically significantly above the OECD average".
TOP SCIENCE RANKINGS
Hong Kong (China)
The UK as a whole was not included in the last Pisa study, based on tests taken in 2003.
The preliminary findings of the Pisa study on science have been released early because of a leak to newspapers in Germany and Spain, but the full results and those for maths and reading skills will be published on Tuesday.
The initial results of the tests put Finland at the top for science, followed by Hong Kong (China), Canada, Chinese Taipei, Estonia and Japan.
The Pisa survey is based on tests carried out in 2006 in 57 countries which together account for 90% of the world's economy.
It tested students on how much they knew about science and their ability to use scientific knowledge to address questions in daily life.
Although the organisers say comparisons between results from these tests and those of previous years are "not strictly valid", they say some countries moved "sharply upward".
These include Canada, Germany, Austria and Denmark.
The organisers give a country's position as being ranked between certain positions because it says with a sample of students it is not always possible to state a comparative ranking with 100% accuracy.
Instead, OECD calculates, with 95% confidence, a range of ranks that the country falls within.
Publication of the study comes just a day after England dropped from third place to 19th in the world in an assessment of reading.
The government says that the Pisa findings show that England is one of the countries with the largest numbers of high-achieving students.
But they also say the study shows a "wide range of achievement, with a large difference between the scores of the highest and lowest achievers".
Boys in England out-performed girls in the way they applied their science knowledge, officials say.
Four out of five students in England said science helped them to understand things around them, but only 38% said they liked reading about science - well below the OECD average.
And only 55% said they generally had fun when learning science - again below the OECD average.
But English students showed a confidence in their science abilities - with 72% saying they could give good answers to science test questions and 64% saying they could easily understand new ideas in science - above the OECD average.
Schools Minister Jim Knight said: "This study shows that we have performed well compared to other countries - and the best English teenagers are amongst the brightest in the world. We're well above average, but we know we need to do more to be truly world class.
79% say science helps them understand things
61% agree there will be many opportunities for them to use science when they are adults
34% said they would like to work in science
38% like reading about science
55% have fun learning science
"It's interesting that while most teenagers think science is useful and relevant to their future lives, not many of them say that science is fun or that they would choose it as a career.
"Next year, we will launch a new communications campaign and programme of science careers guidance to capture young people's imagination by showing them the futures available to those who study subjects like science and technology."
Shadow Schools Secretary Michael Gove, said: "Yesterday we slid down the international reading league table; today we plummeted down the international science league table. External audits are confirming what we have warned about.
"The government has failed to equip our children properly for the future by using tried and tested teaching methods. It has failed to keep us internationally competitive by making sure our exams are properly rigorous.
"We’ve had GCSE science questions in which students are asked if they should use a microscope to look at the moon, for example."
General Secretary of the National Union of Teachers, Steve Sinnott said: "While the results in Pisa 2006 are not comparable with previous Pisa studies there are some mixed messages from these initial findings.
"The ranking represents good news for schools. Nevertheless it has to be asked whether the over prescribed national curriculum in science has led to youngsters saying that they find science less fun than their peers in other countries."