An A grade based on high school grading standards in an AP course would probably be a match for a 4 or 5 score on the AP test.
If A students in AP courses were mostly getting 3 scores, that would raise some questions about the quality of those AP courses at that high school. If A students in AP courses were mostly getting 1 or 2 scores, that should be a big concern about the quality of those AP courses at that high school.