When is it a good idea to repeat some courses you've taken?

If you have the money, time, and willingness to re-take a course that you did poorly in that's when you should repeat a course; be really honest with yourself when you are assessing your situation against these criteria! A core component class is worth retaking because you don't want to be lacking in fundamental skills. Now, there's also the point that you should retake the course to help your GPA (though its diminishing returns if you are in the second half of the undergraduate curriculum) so you can be as competitive as possible for future choices.

Mohammad:

When I went to College, there was one course in my Major, Physical Chemistry, for which I got a grade of D. I chose to re-take this course the next year and I upped the grade to a B. It is often worth your time to re-take a course in your Major if you do poorly the first time. Both prospective employers and graduate schools, if you chose to further your education, will look at your grades and a D or an F can be a problem.

Hi Mohammed,

I would also add that if the class you did not do well in is a pre-requisite to taking other courses for your major you may have to repeat classes. Some classes require a specific grade in pre-reqs. Check with your academic adviser to see if you need to repeat the course in the interest of classes further down the line or to be accepted into the graduate program that you are considering.

I hope this is helpful!

I would add that it depends on your passion and motivation to really learn and apply the subject matter. If you are passionate about it but struggled on the first attempt for whatever reason, then go for taking it again

Hi Mohammad!

If you are having difficulty with courses, the first thing to look at is if these courses are in a career area for which your personality, aptitude, and interests are suited. Here is a good exercise for you to use to find answers. If these courses and the career area do not fit you well enough, you might want to look a another major.
https://www.themuse.com/advice/14-free-personality-tests-thatll-help-you-figure-yourself-out

After you complete the above exercises, it would be a good idea to talk to your academic adviser to discuss what the next move might be.

Also talk to the professors of the courses in which you had difficulty to get their advice.

People are there to offer assistance. All you have to do is ask.

Let me know if and how this might be of help.