The 2013 edition of the survey was a wake-up call for Sweden, which experienced the sharpest drop in results of any of the 32 countries studied over a ten-year span, pushing them below the OECD average.
But Tuesday’s release of the latest instalment of the ranking, covering the year 2015, brought encouraging news for the Nordic nation, as all three subjects showed marked improvements.
Pisa called Sweden’s ability to reduce its share of low performers in mathematics while at the same time raising excellence and increasing its number of top performers “particularly encouraging”.
It also highlighted that Sweden shows one of the highest levels of efficiency in education, producing strong results compared to the number of hours students spend being instructed or doing homework. Only five other school systems in the study had a better ratio of learning time to academic outcome.
“The Pisa result is a show of strength from Sweden’s teachers and students. Hard work has made the difference, that’s known in the classroom, and it has been proven now in the improving competence of those in the ninth grade, and better results across two different knowledge measurements,” Sweden's education minister Gustav Fridolin said in a statement.
The head of Sweden's National Agency for Education (Skolverket) also celebrated the news, with Mikael Halápi labelling the result a "shot in the arm" for the country's teachers, students and principles.
There were however still challenges for the Swedish school system which emerged from the study. The gap between the highest and lowest performing students has increased over the last decade and is now wider than the OECD average. The performance gap between socio-economically advantaged and disadvantaged students has also increased meanwhile.
In addition, the performance gap between immigrant and non-immigrant students in science in Sweden is larger than the average across the OECD countries.
“Gaps are growing. Your upbringing now affects your results more in Sweden than in many other OECD countries. We will never accept that. It is what you do in school that will determine your future, not what home you grow up in. The Pisa result is a happy one, but it calls for policy. We will continue to prioritize more time for teachers, to cut out segregation and give students support in time. No one should be left behind," Fridolin added.
The study also suggests that Swedish public schools are more likely to produce better results than private alternatives in the country.
Though the share of 15-year-old students enrolled in Sweden's private schools more than doubled between 2006 and 2015, students in public schools showed better results than those in private schools after accounting for the socio-economic profile of the students and schools, Pisa noted.
Education agency head Halápi said the new Pisa results require detailed analysis, and tempered some of the celebrations with a reminder that Sweden is still short of its high-point in the rankings from 16 years ago.
“We don't have a full answer for what the improvement is grounded in today. That’s a task for us and the research community to analyze. At the same time we know what contributes to a good school. It’s to do with developing education, getting more people to become teachers and providing the right conditions for the school. We still have a bit to go until we reach the top results of the Pisa study done in 2000,” the Swedish National Agency for Education acting head said in a press statement.