One aspect of the AP Calculus problem that I haven't seen mentioned is the undue incentive students have to enroll in AP courses. Whether or not an AP course is delivered in a fashion that intends to prepare students to pass the AP exam, students may be given an extra quality point toward their grade point average so that an A earns them 5 points rather than the typical 4 points. Many students now graduate with GPAs in excess of 4 as a result. In addition, the advanced nature of the class at the high school level may make it less likely that teachers will award grades of C or lower. I know from the experience of my own daughters that there are AP calculus classes delivered without a specific intention to prepare students for the AP exam, and in those classes few if any students may actually take the exam. And even when the course is designed to prepare students for the exam (which I have also witnessed), the students may have complete freedom to choose whether or not they take the exam with avoidance of the exam more common than participation. I believe that some schools have a policy of requiring completion of the exam, and some may even provide some or all of the costs, but the frequency of passage may still be an unreported or unimportant statistic with regard to the manner in which the school treats the course and grades. I should comment that I know also of teachers who personally take pride in the percentage of their students who take the AP exam and do well on the exam. (Some have faced parental criiticism for the intensity of the courses and the high level of the standards!)
From my perspective, it would make sense to limit the additional quality point in some fashion. School boards, state boards of education and perhaps the College Board might help by setting some standards. I'm not enthusiastic about the extra quality point to begin with, but supposing that is here to stay, the guidelines for schools to award the extra point might require a five year period during which 2/3 of the school's AP calculus students take the AP exam and of those 1/2 pass it with a 3 or better.
It may be that the problems I mention are not widespread. I'd be curious to know whether others are aware of it.