To evaluate how Advanced Placement courses affect college-going, we randomly assigned the offer of enrollment into an AP science course to over 1,800 students in 23 schools that had not previously offered the course. We find no substantial AP course effects on students' plans to enroll in college or on their college entrance exam scores. Yet AP course-takers enroll in less selective colleges than their control group counterparts. Negative treatment effects on college selectivity appear to be driven more by low student preparation than teacher inexperience and by students' matriculation decisions rather than institutional admissions decisions.