I would argue that, no matter what your perception is, school is much more than "sitting in a room for 8 hours". Sure, academic advancement can be accelerated

I would argue that, no matter what your perception is, school is much more than "sitting in a room for 8 hours". Sure, academic advancement can be accelerated massively through home schooling, self-study or tutoring -- and many families take advantage of this fact -- but most school districts offer all sorts of non-academic enrichment programming (even including things like elementary school recesses here) that you don't get otherwise and which result in more well-rounded socialization than you'd get without an intentional effort to augment homeschooling with the same. Also, the sometimes dramatic gulf between private and public school academic rigor means that some private school students are essentially receiving an early college level education during their tween/teen years. This isn't necessarily bad, but it absolutely is more time consuming for most kids who aim for straight As and high test scores, and this in turn impacts their ability to pursue extracurricular activities with seriousness, and without impacting their health/wellbeing. The fact that many public school students are learning slowly means those same students can work outside of school, can pursue sports/arts/etc interests almost full-time, can be caretakers for family members in need, and have flexibility in their social lives. Yes, it's unfair to paint with a broad brush but this is largely true if we're looking at the high achieving population (say, kids who might be expected to apply to Ivy League universities). No matter how suboptimal the pace of academic instruction is at public schools, it's important to recognize that kids are still developing into adults and it's not normal or fair to treat them as adults (from a brain development, psychological and relationship management POV).