Our kids go to Private and yes, it's a lot of money but the education in private is top notch, smaller class sizes and it's traditional learning....not this weird math that is done in the public system. I also believe counter to some here that the most important years of schooling are actually first 5-6 years. I feel like it sets the foundation for the education and more importantly their work ethic. The communication is really good in private school, you know FAST if your kid is shitting the bed and you can fix it early before it becomes a problem. Our oldest had some challenges last year and we knew by 3rd week of september and had it fixed generally by mid-October. I would bet it's not that fast in the public system because of the sheer class size.
There's also lots of intangibles that will help them as well, the cohort they go to school with is really important to challenging them and i've seen that first hand with my oldest. I believe that the network they build will pay off when they get older (their cohort or their cohort's parents). Obviously, there's some downsides to growing up in private school and the people they interact with daily but feel the positive outweigh the negatives.
The cost isn't that bad if you budget for it but if you compare it to the cost of daycare, it's actually the same (ours went to KidsU).