Excellent question. That is why during the application process, the academy requests a copy of your school's PROFILE, along with all the classes you son/daughter are taking. In the profile, it lists the type of classes available; what percentage of students in your school attend college, as well as which colleges they attend. I.e. If your high school has a 65% attending college percentage, which is about normal, and almost all of them go to the local community college or university; that will be ranked different than a school that has an average of 85% going to college. And that school will rank different yet from a school that has a good percentage going to schools like the academy, harvard, stanford, brown, yale, etc....
There's a lot to how they learn to compare apples with oranges and not just come up with a big fruit salad. It's difficult; it's not perfect; but it's a pretty darn good process for what it is. That's how an "UNWEIGHTED" gpa of 3.5 can end up being a 3.84 on the academy's rating. Or, negative happens too and a 4.0 weighted can become a 3.75. Or, you get a school which falls into the "National Average". My son's school doesn't weight gpa for normal kids/classes and those in the IB program or taking AP classes. They do internally determine class rank however. So my son's 4.0 gpa unweighted, remained a 4.0gpa on the academy application. Where some at another school at a 4.8gpa weighted, and a 4.1gpa after the academy reconfigured it. Go figure. best of luck. mike....