Now we have small children, and they're obsessed with reading/writing, numbers, and creative play just like we were as kids -- so they're far ahead of their age group, generally -- but we've kept them out of school so far. We're trying to figure out a path for them through the available educational options, and we're strongly inclined towards more experimental approaches.
It was completely different from her educational experience before that (not unstructured, but still... much more open-minded about education, and smart about guiding students to think about their place in the world) and the experience had a huge positive effect on her life; we are in touch (and in some cases, close friends) with a startling high percentage of her classmates there, and we've met up with (and often been hosted by) UWC classmates in Austria, Netherlands, India, Australia, France, Malaysia, and various parts of the US (and probably some other places I'm forgetting at the moment...). And despite being quite a diverse group, they're generally pretty interesting people to talk to.
I didn't even know such options existed when I was in HS; and probably would have thought it wasn't for me, at that age. But looking back now, I wish I'd gone as well.
And, to be frank, much of what I learned, at least half, while attending public school I learned on my own, independent of classes. But again, I was fortunate. Fortunate to still have faith in the system. Fortunate to have gone to a very high quality high school where I actually could get a decent education and where most of the teachers and faculty put education as their top priority (this is not necessarily the norm). Fortunate to have a home life that encouraged and facilitated reading and learning, as well as acquisition of reading materials. Fortunate that I had acquired maturity ahead of most folks at that age at a time when it was critical. Fortunate that I had not fallen in with "the wrong crowd" of people and ended up dropping out of school or getting into drugs or petty crime or what-have-you.
A lot of kids, smart kids, are not as lucky as I was. And if anything the system is even worse today. Teenagers' lives are more regimented, there's more busywork, there's less trust, the academic bureaucracy is more onerous, it's harder to escape peer pressure due to the ubiquity of social media, and so on.
A lot of academically minded children would have been very poorly served by those schools. People getting to university would have been the children of upper and middle class parents who had money to afford private schooling or tuition or coaching to get into good grammar schools.
And, not to sound too cynical about it, the parents of the "best" children tend to be very involved in their children's education, and might resist an experiment.