Differential Calculus is USUALLY the course used to force you to mentally integrate all of your previous math learning. What students MIGHT be lacking is a solid knowledge of trigonometry. Only you can evaluate your knowledge of algebra, geometry, and trig. To answer your question, there is no reason that the FACTS you learn should take more than about a week or two. There is plenty of reason to believe that the SKILLS you should learn require a lot longer. Doing problems - as long as the answers are also given - might be ok. I doubt it, but its a start. I can remember from my first year of calculus on more than one occasion a problem taking the professor the whole hour to go over. That's not the type of thing you're likely to learn on your own, and it certainly will NOT be something that you can find in a book...and I'd doubt it likely that the superficial treatment they give in summer session will, either. Anyway, for the gifted, willing to study on their own in-depth and for the superficial who just want "the grade", summer school is adequate. For the weaker student (I include myself, I had an A average in high school through trig and calculus) I don't recommend it - IF you're going into the engineering or hard sciences or economics. Otherwise go for it. But you've obviously already decided "what"; the question you seem to actually have is "how". The answer to "how" is do enough problems so that you can pick up any textbook and do 8 out of 10 of any problem set. That requires spending the time to learn the SKILL and having several books with lots of problems and answers as well as lots of examples will be very important.