Earlier quoted context omitted.
I'm from slovenia, a small, former yugoslav country. We don't have special schools for math here, and elementary schools (7-15yo in my time) were the same for all, and you went to the closest school to your home... but our highschool ("gymnasiums" - 15-19) used the grades from elementary school + standardized testing scores to rank students, and somehow best students went to certain schools, 'the middle' got accepted…
This is one school of education. The other is the Finnish model, with no separation. I am yet to see some comprehensive multinational study that would suggest which is better. (Better for the students, or society as a whole?) It’s probably impossible to do objectively. I also feel there is probably quite a difference between these two systems in the effects on the, say, top 0.2%, 2%, and 20% of the students.
Anecdotally, a Finnish friend told me that if you excel at one subject, you are encouraged by teachers to stop doing it, and instead spend more time learning the other subjects.