Nothing illustrates the relentless growth of high school calculus better than the graph of the number of AP Calculus exams taken each year (Figure 1), surpassing 400,000 in 2014. According to NCES data , 53% of the students who study calculus in high school take an AP Calculus exam, implying that roughly 750,000 U.S. high school students studied calculus this past year. By comparison, this past year only 250,000 students took their first mainstream calculus class at a 2- or 4-year college or university .
|Figure 1: Total AP Calculus exams and fall enrollments in mainstream Calculus I. Sources: The College Board and CBMS Statistical Abstracts.|
What happens to the students who study calculus in high school? We know from the MAA study Characteristics of Successful Programs in College Calculus that about one- third of them retake Calculus I when they get to college. Based on AP scores and common policies for granting credit, roughly 200,000 students accept credit and/or advanced placement for their high school work. From a limited study , a clear majority of these students, probably three-quarters or more, do continue on to further courses that build on calculus.
All of these patterns intensify at research universities and elite colleges, where at least 70% of Calculus I students are retaking a course they have already seen in high school, and large numbers of students heading for math-intensive majors skip over Calculus I.
The result has been a dramatic change in the make-up of Calculus I. At most colleges and universities, it makes little sense to teach this course as if students are encountering calculus for the first time; few of them are. It also makes little sense to teach this course as if the students are heading into the mathematical or physical sciences. Nationwide, only 6% of Calculus I students intend such a major . Finally, it makes little sense to teach this course as if this is where we see our best-prepared students.
This last point is clear if we consider how many of the best-prepared students skip Calculus I, but it also is a consequence of what the rush to calculus has done to the middle and high school curricula in mathematics.
In fall 2014 there were just over 1.6 million full-time first-year students enrolled in 4- year undergraduate programs in the U.S. . Assuming that most of the 750,000 who take calculus in high school are traditional college-bound students who will enroll as full- time students in 4-year programs, these high school calculus students will constitute 40–45% of traditional first-year college students. The result is a common belief among parents, guidance counselors, and administrators that every college-bound student should, if at all possible, study calculus before high school graduation. I hear this from college students whose reason for taking calculus in high school was that it was expected of their peer group, and I hear it especially from high school teachers who complain of the tremendous pressure they are under to expand calculus classes and admit students they know are not ready for it.
Because high school calculus by itself has become such common coin, those students who aspire to an elite college or university try to take calculus, preferably BC Calculus, before 12th grade. Figure 2 shows the exceptional growth in the number of students who take an AB or BC Calculus exam before grade 12.
|Figure 2: Number of AP Calculus exams taken by students in grade 11 or earlier. Source: The College Board.|
We do not know the full effect of this movement of calculus into ever earlier grades, but there is strong anecdotal evidence from teachers at both the high school and university level that many of these students are short-changing their preparation in middle and high school mathematics to join the fast track to calculus. Again anecdotally, this appears to be a significant problem when students attempt a math-intensive major where weaknesses in precalculus material can be disastrous.
We can deplore the rush to calculus in high school, but the forces that are sustaining it are formidable. We have neither the authority nor the certain knowledge that would enable us to halt or reverse it. For the foreseeable future, we will have to live with it.
Just in the past ten years, the preparation and aspirations of our college calculus students have shifted significantly. We cannot afford to assume that curricula and methods of instruction that were sufficient for the past will be adequate for the future.
 National Center for Education Statistics (NCES). (2012). An overview of classes taken and credits earned by beginning postsecondary students. NCES 2013-151rev. Washington, DC: US Department of Education. nces.ed.gov/pubs2013/2013151rev.pdf
 By “mainstream” we mean a calculus course that can be used as part of the pre- requisite stream for more advanced mathematics courses. It usually does not include business calculus, but may or may not include calculus for biologists. The figure of 250,000 is an estimate based on data from the CBMS Statistical Abstracts and the MAA study Characteristics of Successful Programs in College Calculus. Approximately 500,000 students began mainstream Calculus I at the post-secondary level at some point in the past year, and roughly half of them had studied calculus in high school.
 Morgan, K. (2002). The use of AP Examination Grades by Students in College. Paper presented at the 2002 AP National Conference, Chicago, IL.
 Source: MAA National Study of College Calculus, www.maa.org/cspcc.
 Source: HERI, The American Freshman. www.heri.ucla.edu/tfsPublications.php