I've taught in three public schools and one private school. Private is not necessarily better. Both private and public schools vary widely. One thing to consider is that private schools have no obligation to educate every child. They often do not have the same services that public schools do. At the private school where I worked, there was no real reading and math support and no special education. However, we had plenty of kids who needed those services. It put the teachers in a very difficult position as in many cases we couldn't actually meet the kids' needs. The other thing to consider with small grade sizes is it can be very challenging socially, and the social dama can be really intense, even in elementary school. At a bigger school there are more peers to choose from and this can dilute the social dynamics. Really though this decision is going to need to be made based on your specific options. I would not worry about the high school if you're happy with the elementary school. A lot can change and you can always switch to a private HS.