Remember that in many cases, the formula looks at the percentage of students who take AP-- not the pass rate. As long as the school has a lot of kids in those most challenging classes, it doesn't matter if they pass or fail or even whether they take the AP tests at all. Just being in the class raises the rating for the school. On the one hand, I'm all for encouraging kids to be challenged, especially as preparation for college. On the other hand, I have seen kids pushed into classes they can't handle simply because they have AP in front of the title.
