Part of the beauty of tests like PISA are that, at least in the US, nobody is teaching to the test because it doesn't have an effect on the students, the teacher, or the school. That makes it an ideal measure because it's less distorted, unlike other tests that may determine student grades & AP scores, college entrance, teacher evaluation, etc.
I believe this is generally the case worldwide, absent some gaming from places like China, who for several years submitted PISA tests only from a few of their best/richest schools (Beijing, Shanghai, HK) as a way to look better internationally, which of course makes it hard to compare to other countries that are testing a broader range of schools.
I believe this is generally the case worldwide, absent some gaming from places like China, who for several years submitted PISA tests only from a few of their best/richest schools (Beijing, Shanghai, HK) as a way to look better internationally, which of course makes it hard to compare to other countries that are testing a broader range of schools.