Several avenues are open to students who wish to study advanced science or mathematics in high school, which include Advanced Placement courses and teacher-designed courses unaffiliated with organized programs. We employ a retrospective cohort study of 4,691 nationally representative college students at 34 randomly selected, colleges and universities to examine the relationship between taking advanced high school courses and students' interest in pursuing a STEM career, while controlling for prior interests and experiences. We are able to distinguish between those students choosing to take an additional year in a science or math subject from those taking Advanced Placement (AP), which is most commonly taken as a second year course, but is increasingly taken as a first year course. We find that the number of years of a science or math subject taken in high school is associated with significant increases in STEM career interest, with results differing by subject. Taking AP courses in science or calculus appear to have no significant impact on STEM career interest over that of other advanced, non-AP courses. Taking calculus, a second year of chemistry, or one or two years of physics all predict large increases in STEM career interest. Additional years in biology and other subjects show no such relationship.