PISA 2018 and Ability Grouping: A Case Against Advanced Academic Programs
Since PISA 2018 data also include the school a student attends, it is possible to gauge whether a given country has more high performing students concentrated in schools. PISA 2018 uses an "isolation index", which provides the probability of finding a high-performing student with classmates who are low-performing, and vice-versa. For example, a value of 0.20 in the isolation index of high achievers means that a student who scores in the upper quarter of the distribution of PISA performance within a country has around 40 percent chance of attending the same school as students who are also high achievers, while this likelihood would have been only 25 percent, if students had been uniformly distributed across
schools. A value of 0 therefore means no segregation and a value of 1 means full segregation. In the graph below, I have shaded the region that includes countries where high-performing students are more likely to be in the same school as other high-performing students compared to the average isolation among all the countries that participated in 2018.
|Above graph modified (yellow and red shading) from
OECD (2019), PISA 2018 Results (Volume II): Where All Students Can Succeed, PISA, OECD Publishing, Paris, https://doi.org/10.1787/b5fd1b8f-en.
Countries in the shaded region are more likely to have high academic ability grouping. How did these countries perform in the test? The ones marked red scored below the OECD average. Countries that group high ability students together perform worse than countries that do not. PISA 2018, a standardized exam, in fact, could be useful.