There is no feasible self-directed study that will lead those kids to the heart of quantum physics, developmental biology, or personality theory of psychology. Granted their parents are loaded with money so they may be able to get more out of it than average.

And sure, im willing to acknowledge that K-12 knowledge concepts are only useful for attaining postsecondary education.

But socialization, problem solving, work ethic for its own sake, and methods of thinking are all valuable in their own rights and all honed in school.