That seems to be why there are some really strange math progression ideas around here:
A. Many students are on the +2 math track, but the high school slows them down to the +1 math track when they reach calculus by forcing them to take a year of AB then a year for the rest of BC, even though students on the +2 math track should be top students in math who can handle BC in one year after completing precalculus. In other words, that school system seems to be inappropriately accelerating many students in middle school math.
B. The idea that students with AP calculus (even with a 5 on the test after an A grade in the course) should always start college in calculus 1 anyway seems to be a common idea on these forums. If combined with A above, that could lead to a student who is initially +2 in the math progression spending three years on single variable calculus that a +0 student is expected to complete in one year in college. (But it seems that this is never suggested for those who complete BC in 11th grade and want to take a college math course while in 12th grade.)
C. The idea that being on the +1 math track is “behind”, so that students try to cram math in the summer or some such to get onto the +2 math track. For example, see this thread: http://talk.qa.collegeconfidential.com/high-school-life/2059047-any-asian-boys-out-there-who-took-calc-bc-senior-year-and-got-into-top-engineering-schools.html .