What is AP (Advanced Placement?)

Advanced Placement is a program in the United States and Canada created by the College Board which offers college-level curricula and examinations to high school students. American colleges and universities may grant placement and course credit to students who obtain high scores on the examinations.

Explanation:

AP Is also High educated children in middle, to high

Pretty sure AP class is an American thing, because here in Australia it's called the GAT class (Gifted and Talented) and provides us with a more broader range of things to do and study. Only the top 30 in our school get chosen to be in the class.