[argonaut]

1) AP exams can be taken independent of whether you've taken the class. A high school freshman can take any AP exam.

2) It's common in competitive high schools for students to start taking AP classes in junior year (or even sophomore year), so top colleges definitely do see AP scores for most of the top 30% of students applying.

For me, AP credit was huge. It let me skip calculus in college and a bunch of other very time-consuming classes (foreign language, etc.). Instead, it cleared up my schedule so by the end of college I was able to take multiple graduate CS classes.