College admissions teams don't accept the GPA from each school as-is. Instead, they look at the difficulty of each course, the school and their knowledge of the students from that school in past years. They actually use their own formulas and recalculate an internal GPA that is specific to that college admissions team. For example, they may only consider core classes and ignore electives. They may or may not count AP courses as part of their formula. In the end, each college makes their own rules about what criteria they will use to compare students.