This statement cracks me up. How by any means how can you tell that your kids are "farther along" than all the other kids.
There are some great private school and some great public schools. I teach in a great pubic high school in a upper class area. We have a great number of kids that go to private school for K-8 and than transfer to our public HS due to all the "extra" classes available. We offer 5 languages, an engineering academy, a working public TV studio, a IB program, over 20 AP clasess and the list goes on, .
Many of the students that come to the HS with their expensive, wonderful, private school education often struggle with the social aspect of school. Many provate school are very small with the same kids moving from grade to grade. They never learn to adjust to new environment and so on.
I would advise you to spend some time in both environments. Tour the school during school hours when students are engaged in learning. Don't just visit during "open house" when everyone puts their best foot forward.
Don't go by test scores alone. They only tell a small part of a schools picture. Look at the students interactions with the teachers and other students. Look at the creativity in the clasroom -are the walls decorated proudly with the students work. Look at the "extras" your child might enjoy. If they are into performance - look at the arts programs, if they are into sports - check out the facilities and attend a few games.
Whatever you decided respect others decisions and realize what is best for your family is not the best for everyone.
Trust me, when your children are scoring in the 80-85% nationally in reading, math, science and social studies on the ITBS vs. what the scores from the local elementary school are...They are ahead.