Phil Parker

Imagine you are a policymaker tasked with overhauling your country’s education system. You are faced with a bewildering list of competing claims, all advanced with absolute certainty by proponents. Should you listen to the economists who want to expand school choice? What about the trendy calls to replicate the ‘Finnish miracle’—should you try to produce a near carbon copy of the Finnish system? What about a return to old fashion tracking like the Germans and the Dutch? Empirical data exists but most of the best stuff is on local interventions that are unlikely to tell you much about how a particular policy will affect the whole education system. 

This is why high quality, multi-cycle, and multi-nation studies like PISA are so valuable. They allow policymakers to compare countries with different policy environments on a common metric; literacy, numeracy, and science achievement. Policymakers can also compare results across time to see how the introduction of some policy has benefited or harmed the performance of a country’s students. 

Policy Question: Does Achievement Stratification Help or Harm?

Using PISA we asked: do countries that stratify their schools by academic achievement do better in PISA tests than countries that do not? Stratification refers to lots of different policies such as school tracking, private schooling, selective schools, magnet schools, school choice polices and school catchment area policies in countries that are highly geographically segregated by income and wealth. All these policies result in higher-achieving students being schooled together and separately from lower-achieving students. You can read the full text of our article here.

There are many good reasons for implementing stratification policies. Perhaps smarter children can only flourish when educated among their peers. Teachers may stratification be able to target their teaching to the level of the students. School choice may provide parents with latitude to select a school that has the right fit for their child. But stratification may also have negative effects. 

Poorer performing students may enjoy the help of smarter children. And smarter children may gain a richer understanding of a topic by teaching it to other students. In addition, a now extensive body of research shows that children educated in selective schools have poorer motivation, worse self-beliefs, and lower academic interest than similarly able peers educated in comprehensive schools. And these effects are worse in countries with more stratification.

What We Found

With these competing views, we collated data from five cycles of PISA to look at the relationship between the amount of stratification in a country’s education system and their performance. We also looked at whether increases or decreases in stratification over time were related to improvements or declines in average academic performance. The figure below tells the story. Countries where stratification increased experienced declines in average performance. 


Our research argues that policies that increase achievement stratification are associated with declines in average academic performance. Should policymakers change school systems based on our research? On its own: no. Yet the results are illuminating and, taken as part of a larger body of research, suggest policymakers should aim to create more egalitarian school systems.

About the author(s)