PISA 2018 and Ability Grouping: A Case Against Advanced Academic Programs

The "Standards Movement" in education works on the premise that schools are not performing well because we have not tested the students enough. It is obviously possible for schools to not perform well for reasons other than not having exams. However, the disdain for the "Standards Movement" should not be equated to a disdain of standardized exams. Standardized exams, after all, are assessment tools, and it is still possible to draw useful insights from the exam scores, if we know how to look for important clues. For example, there is an unfounded notion that ability grouping, which leads presumably to a much more homogeneous classroom, can produce better learning outcomes. One can check if this notion holds true by looking at an international standardized exam like PISA 2018. PISA 2018 shows that this is not true.

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.