I had my son in public school until 3rd grade, but the school didn't have a gifted program and had no interest in differentiating the kids in any way. We ended up at a private school that didn't specifically market itself as gifted but said on it's website that it could handle gifted kids. There we found that kids were grouped by ability rather than age for reading and math. In addition there seemed to be a higher percentage of gifted kids, many of whom are also refugees from public school. We've been very happy. Before we left, my son was miserable at school. Now he loves it.
Obviously the price of public school can't be beat, and if it works that's fantastic. But if it doesn't I think private is a great option and it doesn't have to be fancy (you need the teachers more than the indoor swimming pool!)