One big factor is the ubiquity of phones / social media which is a huge distractor and makes it hard for kids to focus and learn (I say this as a parent with young kids).
The other big factor is the involvement of the parents after school. One thing about places like HK, Singapore, Japan, China (big cities like Beijing, Shanghai), all of which score high on these tests, is that the kids don't play after school -- they do extra math (and I'm talking elementary school, not high school--the pressure is much worse in HS). And the same is true of many such immigrant families in the US. In my experience (having lived for many years in those countries, and now in the US), this is a much bigger difference maker than whatever teaching methods might be used in school. But then there's also the question of how much you want your child to be able to enjoy just being a child, and how young do you want to put them in the pressure cooker of testing - get into better school - testing - get into better HS - testing - get into better college - testing - get job that makes more $. They'll experience all that soon enough -- do you really want them starting at age 7?
The other big factor is the involvement of the parents after school. One thing about places like HK, Singapore, Japan, China (big cities like Beijing, Shanghai), all of which score high on these tests, is that the kids don't play after school -- they do extra math (and I'm talking elementary school, not high school--the pressure is much worse in HS). And the same is true of many such immigrant families in the US. In my experience (having lived for many years in those countries, and now in the US), this is a much bigger difference maker than whatever teaching methods might be used in school. But then there's also the question of how much you want your child to be able to enjoy just being a child, and how young do you want to put them in the pressure cooker of testing - get into better school - testing - get into better HS - testing - get into better college - testing - get job that makes more $. They'll experience all that soon enough -- do you really want them starting at age 7?