I'd say that is believable. There is a strong correlation between parental income and a child's SAT score. So you could probably get a rough estimate of a public high school's average SAT scores by looking at the average income in the surrounding areas. I was looking at a couple public high schools in California, and there some where it looks like the average senior is graduating with test scores close to the top 10%. I'd expect some schools have uncommon success placing seniors into elite colleges because they have a very talented student body.