I am a freshman in college with a double major. Most of what I know I am self taught in. I have talked to different professors about what courses I should take and some of them recommended taking courses that I already know. Some said to do this for an easy A and this does make sense. But others say I cant really learn things on my own. I tried proving them wrong. I did this by testing out of all of my required calculus classes, differential equations, and elementary classical physics I and II (which is the first level of calc based physics). Even after testing out of classes that people said I couldnt do on my own (many have told me that I couldnt learn calc II and III and differential equations on my own and my physics professor doesnt think Im ready for modern physics even though I already read the whole textbook and done almost every problem) I still have people tell me I should take the courses. I also had a professor tell me to take quantum mechanics I and II even though he knows that I know this already. A question that has been bothering me for a long time is, whats the difference between self teaching and taking courses? Why should I take a course in classes that I already know instead of testing out of them?