HS graduation rates vary widely from school district to school district in the US. We have no national curriculum and funding is extremely different from town to town. Plus, in other countries, particularly in the EU, students are tracked at a young age. Some do a technical track and graduate at 15 or 16, while others pass a college entrance exam and do 2 years of college prep work before matriculating at a university. Here, we don't have that choice, although there are technical high schools. But even then, you are in school until 17 or 18.
The best example I can give is that the HS I taught at in AZ had a 12% drop out rate. It was high for my district, but we had a lot of non-English speaking kids who didn't get the services they needed. And this was a really good school district . The HS my kids went to had about a half a percent drop out rate, as does the school where I live now. The high school in the city where I am doing my counseling internship has a 50% drop out rate. It all has to do with poverty and funding.