Today I met a student from last semester. He was a returning student who had forgotten most of his math. He came to me in the beginning of the semester to ask how he could do well in the course. Of course I told him. During the first few weeks he considered dropping, because had to learn the new material and much of the old material. He worked very hard for the first half of the semester, and less hard once he caught up.
The next course, precalculus, is a hard one, and when I saw him, I asked how he was doing. He said he had a 99 average and was a bit worried because it was too easy. I wish more students had that problem.