Went to #548 from elementary to middle, tried to transfer to #57 but failed interviews (I think I went up to round 8), spent one year at #1523 and then successfully got into #57 the next year.
I think that I was very lucky to get in and it was the most valuable part of my overall education. It taught me many things. That there are other people who are much smarter than me and it's OK (and may be I'm not smart enough to do math as a science for a living). A lot of mathematical intuition, about very non-mathematical things, all the way to poetry. How to structure your thought, attack your own arguments and prove something - or discover that the proposition you were trying to prove was false to begin with. (Apart from state-mandated math program, we had our own, with special lessons, where we wouldn't need to calculate or find anything. The only activity was to try and prove theorems and lemmas that you didn't know the proofs of.) That despite years of experience of being a weirdo and a nerd I can finally find a social circle where I can feel normal and accepted. In fact, 15 years after graduation we still have an active Discord server where 8 people were streaming some video games and chilled in voice chat just last night.
So, I think that when you filter kids not only by some "IQ-by-proxy" tests but also by what later get the name "culture fit", and let them coexist together for a few years, it can be a very powerful and life-changing thing. Not everyone such a good experience, of course - but a lot of us did.
I suspect that there's much more of us here in the comments in general than you would recognize. As well as all other post-soviet math-schoolers. It's exactly the kind of education and attitude that makes a career of a senior engineer at FAANG or CTO at a VC-backed startup not only easy in a technical sense, but also a perfect cultural fit.
I think that I was very lucky to get in and it was the most valuable part of my overall education. It taught me many things. That there are other people who are much smarter than me and it's OK (and may be I'm not smart enough to do math as a science for a living). A lot of mathematical intuition, about very non-mathematical things, all the way to poetry. How to structure your thought, attack your own arguments and prove something - or discover that the proposition you were trying to prove was false to begin with. (Apart from state-mandated math program, we had our own, with special lessons, where we wouldn't need to calculate or find anything. The only activity was to try and prove theorems and lemmas that you didn't know the proofs of.) That despite years of experience of being a weirdo and a nerd I can finally find a social circle where I can feel normal and accepted. In fact, 15 years after graduation we still have an active Discord server where 8 people were streaming some video games and chilled in voice chat just last night.
So, I think that when you filter kids not only by some "IQ-by-proxy" tests but also by what later get the name "culture fit", and let them coexist together for a few years, it can be a very powerful and life-changing thing. Not everyone such a good experience, of course - but a lot of us did.