My husband thought long and hard about this decision, and we still revisit it every few years.
Husband and I went to Catholic schools for elementary, high school, and for me undergrad and post-grad. We were *certain* our kids would go to private school!
When the time came with my first one, we sent him to the neighborhood public school for kindergarten, to get "one free year" out of the system (we had both gone to public kindergarten) and just in case he needed to repeat kindergarten (he was a young kindergartener with an August birthday), we could switch schools.
Well, we fell in love with our little public school! Before first grade, my husband interviewed the principals of the public and private schools we were interested in, and asked a lot of questions about education style and programs. The public school won hands down for its educational philosophy and it's extra programs (at the private school it was languages and arts, at the public was geography--I think an understanding of Geography is critical in today's world.)
When it came time for middle school with the oldest, we thought we switch to private instead of sending him to the public neighborhood middle school. Then I found a K-8 school that would accept students from other neighborhoods if they met certain criteria. He got in, and it was the best thing for him. He REALLY blossomed at this school, it's fantastic! I used to hate the idea of switching at middle-school age, but for him, I think it was great for him to get out with new people and a new environment.
Now he's been accepted to the local magnet high school. Its programs are so great, it's amazing! The ASL is in Hawaii right now in the national competition--and they've won most years in the past!
My daughter is still at the neighborhood K-6 school, and this year was accepted to their gifted program and she is LOVING it! She gets to study all kinds of interesting subjects in depth.
I like the public school system because of the variety of programs for different learners. The boy did a Gaps program when he needed extra help in the early grades, and now is in the honors at the new school. My daughter has two IEPs--one for speech and one for gifted.
I also appreciate the diversity. My Catholic school was very homogeneous. My kids' attend school with a variety of people from different backgrounds and even different counties. I feel they have a broader understanding of their community, and little a less apprehension about people different from them.
Be careful just looking at test scores--because my daughter's school has a lot of ESL students, sometimes that is reflected in the scores. It doesn't affect the quality of the education she receives. Sure, any school that can pick and choose who attends are going to have fantastic scores. I also suggest one-on-one interviews with the principals, like my husband did, and talk to EVERYONE you know with school-age children. That's how I found out that lots of kids coming from the private schools to the public found themselves behind the rest of the class.
Good luck with your decision.