Like Terence I also had "out of band" classes and free time to read advance material in both primary and high school.
During that period Australia also had good federal and state programs for clustering advanced kids on yearly subsidised specialist camps - optional and free if parents couldn't afford to chip in.
I bumped into him at the same time Paul Erdős was doing the rounds and hanging out with anyone that might show promise.
If the goal is to map the global status quo on education, the answer is to go country by country and ideally visit as many as possible.
This was the path mayself and others followed when we wanted to map the current state of global mineral and resource extraction. ie Grind.
Particularly during the Cold War years emphasis was placed by major powers on intellectual and physical achievements, countries dedicated resources to hothousing swimmers, runners, chess players, musicians, etc.
I'd add to that a number of peer children with various gifts I grew up with never wanted to (for example) play the violin ever again. Push too hard and you can easily blow it.
More generally, advancing children en masse is likely still "done best" by Finland, a country considered by many to have the best general education system. All the teachers are university educated in <subject> + "education" (the act of educating) and they adopt a policy of stability, resourcing, active teaching (teacher lectures class) and near equal time for student activity (half the class time spent by students doing stuff for themselves related to topic).
Policy wise, it's not all about the super brains - the trades are hard and demand skills, it's good to have parallel streams; applied STEM for some, apprentiships for others, AND (in my opinion at least) a mixing of the two - giant autonomous 240 tonne trucks don't build themselves, someone has to lathe out massive hydraulic cylinders and control rods and levers that others have to control via funky math stuff.
Here in W.Australia the capital city Perth has a number of specialist high schools - Performing Arts ones that feed into WAAPA (post high school level performance), an aviation focused high school my son attended where each intake year builds their own aircraft to fly ( https://www.kentstreetshs.wa.edu.au/aviation ), etc.
These are state schools (free) that are general schools (like all the others) with additional Specialist Programs.
There are some 190+ odd countries about the globe, it would take some time to table out the education programmes in each.
Like Terence I also had "out of band" classes and free time to read advance material in both primary and high school.
During that period Australia also had good federal and state programs for clustering advanced kids on yearly subsidised specialist camps - optional and free if parents couldn't afford to chip in.
I bumped into him at the same time Paul Erdős was doing the rounds and hanging out with anyone that might show promise.