I have a son soon turning 6 who is cramped in a small classroom all day, without any chance of playing outside. He does learn there how to focus and be patient and he draws a lot there. He also has some pals and even plays with the girls when there are no other boys around. He is sometime critical of the schooling system himself, saying they don't really teach him there, but he may have picked that up from something I said to his mom.
What I try to do to keep a healthy balance is to take him out early each day if I can manage it, and if it's not too wet or too cold we go out for an exploration walk in nature. We can walk by the riverside which is very close, and then reach some "uncharted" land with hidden "islands". He finds stuff on the ground and we meet animals and discover plants and nice stones.
Lately he displays a strong interest in money and how to make it. He comes up with fantastic ideas, like setting up a "shop" and successfully selling us and his grandparents things that we already own. He is so fascinated with the subject that he learned to multiply 5 by 10 just to figure out how he can get a note of 50. He is quickly getting around the point that people give money in exchange for products and services, and is now offering us valuable services that will generate more money for him.
Last year he was attending a private kindergarten where he could play outside and have more exploration time and one-on-one tutoring. But also then we had to keep a balance and make sure he gets input from me and my wife. I used to take him to watch some great movies and showed him some cool stuff on the web. We taught him how to ride a bike, how to build complicated lego spaceships using the instructions, and then how to build whatever you want without any instructions. I also took him with me to my office a couple of times, to get a feeling of what adults do when they say they go to work. I remember my dad taking me to work as kid - these are some of my longest lasting childhood memories, and I believe the same goes for my children.
There is a strong social case in favor of going to kindergarten and school, and I don't want to deprive my kids of that. At the same time, I had attended what was considered one of the best schools in my country and ended up feeling like I wasted 12 years learning nothing useful or meaningful. That said, I realize today that many of my classmates went on to do some interesting stuff in their lives, and I could find a footprint of our school in some of the choices taken later in life, when, as young adults, a subject or a cause attracted some of us more than others who attended other institutions.