More than 10,000 fourth and eighth graders in Sweden took part in the study.
12 out of 49 countries outperform Swedish pupils in reading ability but Sweden lies above the EU/OECD average.
The results from the last Trends in International Math and Science Study of fourth and eighth graders in 2007, saw Sweden's ranking for science fall farther than any other country surveyed. Today, five years on, the results from the latest study show that knowledge of science here has improved for primary school kids, but math performance continues on a deteriorating downward spiral.
This on a day when the results of another major survey, called the Progress in International Reading Literacy Study, or Pirls for short, which measures reading skills amongst 4th graders also showed that the overall picture for Swedish pupils' performance is more downbeat than that ray of light in the science field.
Education Minister Jan Björklund told a press conference following the publishing of the results:
"The results are worrisome, however, they are slightly better than expected. I would say. My overall conclusion is that school reform must continue with full force."
Björklund said that he was encouraged by the results in the Timss's study, pointing out that science results have gone up while math has not further deteriorated. He did admit though, that Sweden's results measured over time are much worse than those of other countries.
The Pirls reading study covered 4,700 young Swedes in fourth grade.
Sweden's National Agency for Education, Skolverket, reported that the study shows that reading results have worsened since the last study in 2006, but remain above the EU/OECD average. Fewer now reach the highest levels in reading with more on the medium and good basic level compared to previous Pirls surveys. This says Skolverket, is primarily down to pupils becoming worse at reading fact-based texts.
In the Trends in International Math and Science study, math results for 4th graders stayed the same as 2007, but under the EU/OECD average, while in science there has been an improvement for fourth graders with results better than 2007 and above the EU/OECD average. This, says Skolverket, is the first time an improvement has been made in an international survey since the early 2000s.
For eighth graders though, the science results are on the same level as five years ago but under the EU/OECD average, while in maths in that age group, the results have deteriorated further since 2007.
The analysis also shows that Swedish pupils learn less between grades four and eight than students in other countries, social background is also a factor, with children with more educated parents performing better than those with parents with less education. Teaching was also a factor with differences in how Swedish teachers instruct compared to those in the rest of the OECD.
Skolverket's Director Anna Ekström told Swedish Radio News:
"In general, we see quite often in this study, that Swedish teachers use fewer and fewer examples of different kinds of learning variants. We also see that Swedish teachers sometimes use textbooks more than teachers do in other countries."
Union leaders, including Eva-Lis Sirén called on the government to allow schools to allocate more cash to help weaker students, and give teachers more time to spend in the classroom.