<p>
</p>
<p>Students taking AP calculus BC do tend to be a self-selected group of top students in math, so the assumptions about “average” students does not really apply to that group. A fairly significant percentage of them are likely to be fully ready to go straight to multivariable calculus and differential equations.</p>
<p>Students taking AP calculus AB tend not to be as strong on average, so such students may be more likely to need to retake the course covering the same material as their AP course. About 2.7 times as many students take the AB test as the BC test, but if you count only those who score a 5, that shrinks to 1.4 times as many.</p>
<p>Note that 5-on-BC students are only about 1.5% of high school graduates (probably 4.5% of the four year college bound), while 5-on-AB students are only about 2.1% of high school graduates (probably 6.3% of the four year college bound), so these students are not “average”. Counting all of those who score 3 or higher, AB passers are about 5.2% of high school graduates (probably 15.6% of the four year college bound), while BC passers are about 2.6% of high school graduates (probably 7.8% of the four year college bound), although you will probably agree that those who scored 3 are less likely to be ready to move ahead compared to those who scored 5.</p>