There are typically four factors for copyright infringement: 1) the amount of the work copied (the more copied the more likely it is to be infringement or the more "key" the copied elements are to the original work, the more likely to be infringement; 2) the nature of the work (the more creative the original work the more likely to be infringement; 3) the purpose of the copies (educational purposes are less likely to be infringement than commercial purposes) and the market effect (if the copies take away from the market for the original it is more likely an infringement).
Please consider the following question: does the practice of quoting from various writers as part of a term paper raise legal or ethical concerns?
I think that it depends on the amount of material in the term paper that is quoted from various writers directly would determine if legal/ethical concerns are raised given the the four factors for copyright infringement that you mentioned. If someone is writing a paper full of long quotes from an author(s) just to fill space to get to the number of pages minimum for the assignment, that definitely would raise an ethical concern for me. According to ...
The four factors of copyright infringements are examined.