What many entering frosh find in college is not so much that the material is harder, but that college requires much more self motivation and time management than high school. Precalculus or calculus 1 in college covers material at twice the speed that high school precalculus or calculus AB covers it, for example. There is also much less hand holding in college; students are expected to keep up on the reading and be prepared for class on their own. And they have to come to class on their own without the instructor taking attendance.