Around here $10k a year won't get you a really good private school - double that for high school and you MIGHT get them into a college prep high school. You'd be better off with a good public school and $10k in enrichment.
I recently faced with similar decision.. we are in a "good" school district. rank top 5% in NJ (but we know what those ranking meant, therefore just take it as a good school system).
However, I do know that it is mainly because of the parents, extra help at home. (I have no plan to to go into the parenting vs school education debate). If I take away the extra help, I think the education is decent and I spent some time to talk to the teachers last year, I think many are just doing a decent job, not great. Hence I decided to let my kid try private schools. She was accepted in both, one charged over 31K and another over 21K tutition alone, not to mention transportation for 3k...
One attaction of the private school for me is that they group the kid by ability, say if my kid were in 6th grade, if her Math is at 7th grade level, but LA is at 5th grade level, then she would take 7th grade Math and study with the 5th grade kid for LA...
Then I thought about the 35K, I may as well use the money to get a private tutor to give daily help ...another major reason is that DH thought I better spent the money for college...
Obviously, there are other advantages in private school too, smaller class size and they may be able to learn as an individual thinker..
difficult choice... but I can tell you that if it were 10K, it would be a no-brainer.