On 8 September 2026 the OECD released the results of PISA 2025. More than 760,000 fifteen-year-olds in 91 countries and economies had sat the tests, standing in for about 33 million of their age. Within hours the headlines had a winner (Singapore topped reading; four Chinese provinces and cities combined, Beijing, Shanghai, Jiangsu and Zhejiang, topped maths and science), a loser, and a verdict on every minister. The OECD itself reported that its member countries had reached the lowest average levels it has observed in science, reading and mathematics.
Look at the same table another way. Kenya and Rwanda took part, with maths scores of 326 and 312 against an OECD average of 463. Is that a verdict on their teachers? On their wealth? On how many 15-year-olds are in school to be tested at all? The table cannot say. Someone who has studied comparative education reads a league table the way a doctor reads one blood test: as a number worth having, with a long list of things it does not settle.
The second half of the subject is the argument. Should children be sorted into different schools early? Should families be able to choose, with public money? How much should be tested, and what should the results cost the people being tested? Serious people hold every side of these, and the evidence is real but narrower than anyone's slogans.
Schooling looks different everywhere, but the differences come from five choices every government makes. Who runs the schools: the state, local authorities, churches, private operators. Who pays: taxes, fees, or both. Who chooses: the family, or a catchment line on a map. When children are sorted: by 10, 12, 15 or never. How learning is checked: a national exam, school-based judgement, a sample survey. Two systems that look alike on three of these can differ sharply on the other two.
| System | A few facts that mark its design |
|---|---|
| Finland | Comprehensive schools phased in 1972–77; compulsory schooling starts at 7; teachers hold a master's degree; no high-stakes tests in basic education; the first split, academic or vocational, comes after about age 15. |
| Singapore | Primary national exam (PSLE) after six years. From 2024 the old Express and Normal streams gave way to Subject-Based Banding, with pupils in levels G1, G2 and G3 that can differ by subject. |
| Japan | 6-3-3-4 structure; nine compulsory years; secondary entry by school admissions exams; roughly six in ten pupils attend private cram schools (juku). |
| Netherlands | A 1917 settlement made religious and other private schools publicly funded; in 1997 more than 70% of pupils were in privately run, publicly funded schools. Tracking is early and has strengthened since the late 1990s. |
| Chile | A universal voucher system from 1981; in 2008 a law gave 50% higher vouchers for priority (poorer) students. |
| India | The National Education Policy 2020, approved 29 July 2020, replaced the 10+2 shape with 5+3+3+4 and set mother-tongue teaching through grade 5; the three-language rule is contested, especially in the south. It aims at public spending of 6% of GDP. |
| Kenya | Free primary schooling returned in 2003; the 8-4-4 structure (1985) gave way to a competency-based 2-6-3-3-3 curriculum from 2017; exams close primary (KCPE) and secondary (KCSE). |
Sources in the list at the end. The Singapore, Japan, Finland, India, Kenya and Netherlands entries are dated descriptions of design, not rankings.
PISA tests 15-year-olds who are in school, using a sample of schools and pupils in each place. A score is an estimate from that sample, so two neighbours in the ranking a few points apart are, statistically, often tied. The test is also a particular choice: it asks students to apply what they know to unfamiliar problems, not to repeat a national curriculum. TIMSS, which tests 4th and 8th graders on curriculum-linked maths and science, asks something different, and rankings can shift between them. And PISA says nothing about children who are not in school at 15, which matters most where enrolment is lowest.
Scores from the OECD's PISA 2025 results (released 8 Sept 2026) as reproduced in the public tables. The tie threshold is your own choice, a stand-in for the margin of error, which differs by country. A * on the United States means a sampling standard was not met.
Without JavaScript: PISA 2025 mathematics, OECD average 463: B-S-J-Z 612, Singapore 563, Japan 525, Estonia 508, United States 463, Brazil 377, Kenya 326, Rwanda 312.
Notice what the bars do and do not carry. B-S-J-Z is four rich, urban Chinese jurisdictions, not China. Estonia sits near the top of Europe in all three domains. Finland, first in reading and science and second in maths in 2003, scored 474 in reading, 469 in maths and 504 in science in 2025: still above the OECD average in all three, but no longer in the top tier. Compared with 2022, science held broadly steady, but among the 23 OECD countries that took part in both rounds the average fell by 16 points in reading, 11 in maths and 5 in science.
Every ministry wants to copy a winner. The honest reading is that top performers differ more than they agree. Finland has almost no high-stakes testing before 16 and a master's-level teaching force. Singapore has a national exam at the end of primary school, at about 12. Japan has a tradition of teachers studying lessons together (lesson study) and a large private tutoring industry beside the schools. Estonia, a small country, scores near the top in Europe. Shared features are modest: a well-prepared teaching profession, a coherent curriculum, high expectations. Even those are descriptions of correlation, not tested causes.
Comparative scholars warn against "policy borrowing": lifting a feature out of a system whose parts depend on each other. A national exam works differently in a country with strong teacher trust than in one without. The question to ask of any success story is what else was true of that country, and whether the result also appeared before the policy.
Tracking means separating children into different schools or classes by measured ability. Germany assigns pupils to a secondary school type after about grade 4; the Netherlands and Switzerland sort around the end of primary; Finland waits until about 15; the United States keeps secondary schools comprehensive but sorts inside them with advanced classes. The cross-country evidence that early tracking increases inequality in outcomes is among the stronger findings in the field (Hanushek and Woessmann, 2006), while its effect on the average is unclear. Economists who re-examined that work have questioned how robust the statistical result is.
One reason the debate does not settle is that sorting at 10 is a noisy act. The next toy shows how noisy, for a given test reliability. It assumes ability is fixed and that a single test decides, both simplifications: real systems use grades, teacher opinion and parents' choices, and a child's ability changes.
Computed live from 20,000 simulated pupils with normally distributed ability; observed score = true ability plus test noise. Illustrative reliabilities, not any real exam's.
Without JavaScript: with reliability 0.80 and 30% of places academic, about a fifth of the truly top 30% land in the lower track.
All systems ration places somehow. A catchment line rations by address, which means by house price. School choice rations by family preference: public money follows the child (vouchers), or independent state-funded schools compete with the local ones (charter schools in the US, free schools in Sweden and England, the Dutch system of private schools funded by the state). Defenders and critics both point to evidence, and the evidence differs by country.
Predict each result before you reveal it. These are lottery-based or large-scale studies, chosen because they are the best-known tests of the idea.
Each result is one study in one place and time. Programme design, the quality of the private schools available and the comparison group all matter.
Without JavaScript: Colombia (PACES lottery): gains of about 0.2 standard deviations after three years. Chile (1981 vouchers): no clear average gain, more sorting. Louisiana (scholarship lottery): worse test results for winners. Milwaukee: higher graduation and college-going in a 2013 study.
Sweden is the most-watched middle case. Its 1992 reform allowed independent schools with public funding; by 2008 over 10% of pupils attended them. One study found competition improved results in nearby public schools; critics, including the researcher Susanne Wiborg, argue the system increased social and ethnic segregation. Both claims can be partly true: a benefit for the average and a cost for the mix.
Exams do two jobs that pull against each other. They give pupils, parents and governments information; and, when stakes are attached, they steer behaviour. Campbell's law says that the more a number is used for decisions, the more it bends the thing it measures: teaching to the test, narrowed subjects, schools shedding hard-to-teach pupils. Yet the information is valuable. Disaggregated results show which groups are being left behind, and in the US, studies of the 2002 No Child Left Behind law (Dee and Jacob, 2011) found maths gains in the middle grades but not in reading.
A single score is also noisy for an individual. If a test has a standard error of measurement of 4 marks and the pass mark is 50, a pupil whose true level is 52 passes only about 69% of the time. A cut score turns a smooth scale into a cliff.
Each bar: chance a pupil whose true level sits that far from the cut passes on one sitting. SEM = 10 × √(1 − reliability). Normal errors assumed.
Without JavaScript: reliability 0.90 gives SEM about 3.2; a pupil 3 marks above the cut passes about 83% of the time.
Finland's answer is to hold no high-stakes tests in basic education and to rely on teacher judgement and sample-based checks, concentrating the one big exam (the matriculation exam) at the end of the academic upper secondary track. Singapore, Korea, Japan and China (the gaokao) use exams as gates and have large private tutoring industries around them. These are different bets about whether the information is worth the pressure.
A good test of understanding is to state a view you do not hold so its holders agree you got it right. Pick a topic and a side. The tool shows the position as its defenders put it, the evidence they rely on, and what would count against them. Note which parts are about facts and which are about values.
Tracking, for: teaching can be pitched to the level; strong pupils are not held back; vocational routes carry dignity. Against: early sorting is noisy and follows family background. Choice, for: families know their children and exit pressure improves schools. Against: skimming and segregation. Testing, for: information makes gaps visible. Against: stakes distort what is measured.
Comparing countries is the only way to see that the way we school children is a choice, and it is a weak way to learn which choice is best. Read a league table as a measurement with error bars, ask what else was true of a winning country, and keep apart what the evidence shows from what a society wants its schools to be for.
Try this: take any education headline that cites a ranking and find the actual scores. How far apart are the countries it contrasts, and are they close enough to be tied? Then write the strongest argument against the policy it recommends.
Sources. OECD, PISA 2025 Results (Volume I), released 8 September 2026, and the OECD Secretary-General's launch statement of that date; the PISA 2025 country tables as reproduced in public references, retrieved November 2026; Hanushek and Woessmann, "Does educational tracking affect performance and inequality?", Economic Journal, 2006; Duflo, Dupas and Kremer, "Peer effects, teacher incentives and the impact of tracking", American Economic Review, 2011; Oakes, Keeping Track, 1985; Friedman, "The role of government in education", 1955; Hsieh and Urquiola, Journal of Public Economics, 2006; Angrist et al., on Colombia's PACES vouchers, American Economic Review, 2002; Abdulkadiroğlu, Pathak and Walters on the Louisiana Scholarship Program, American Economic Journal: Applied Economics, 2018; Wiborg on Sweden's free schools; Dee and Jacob, Journal of Policy Analysis and Management, 2011; Campbell, 1979; national structure facts from the Finnish, Singaporean, Indian (National Education Policy 2020) and Kenyan government and reference descriptions. Every figure in the interactives was computed in node. This piece reports evidence and takes no side on the policies it describes; a ranking's difference in score is not a measure of how good a teacher or school is.