I know what you are saying, but I don't think it works that way. The last article I posted said something about China possibly cheating by manipulating the population where the students come from, but that would be cheating, and an anomoly, not the norm.
How does PISA select a representative sample of students?
To provide valid estimates of student achievement and characteristics, PISA selects a sample of students that represents the full population of 15-year-old students in each participating country and jurisdiction.
This population is defined internationally as 15-year-olds attending both public and private schools in grades 7-12. PISA requires a minimum of 4,500 students from a minimum of 150 schools in each participating country and jurisdiction. Within schools, a sample of 35 students must be selected in an equal probability sample unless fewer than 35 students age 15 are available (in which case all students are selected). PISA requires that students in the sample be 15 years and 3 months to 16 years and 2 months at the beginning of the testing period. The school response rate target is 85 percent for all countries and jurisdictions. A minimum participation rate of 65 percent of schools from the original sample of schools is required for a country or jurisdiction’s data to be included in the international database. PISA also requires a minimum participation rate of 80 percent of sampled students from schools within each country and jurisdiction.
Program for International Student Assessment (PISA) - Frequently Asked Questions
If you think about it, it would be unlikely that an international effort to quantify education statistics would have such a glaring flaw in sample selection. That's basic statistics fundamentals.