When teaching undergraduate students, I find freshmen students to be mostly unaware with the idea of including evidence to support the author's opinion. That is, they write something like:
Leaders should be friendly and support those in lower positions in the organization. Being friendly makes others like you and that makes them work harder.
Where it should be more like:
Goleman (2000) wrote about affiliative leadership in which the leader focuses on the emotional connection with the followers. In the ABC case, the leader is likely to be well served by using affiliative leadership due to the fact that workers who feel a strong emotional connection with their manager are known to push themselves harder in order to gain the approval of the manager (Jones, 2008). This implies that the leader should not only be affiliative but should also withhold compliments from the subordinates in order to maximize output.
I remember my teachers telling me the guidelines was 80/20. 80% of the writing should be from the student and 20% should be from external sources, which support the student's opinion.
Meanwhile, I have read quite a few papers from students where they basically have a citation for every sentence. This makes me wonder if they actually know much. After all, if 80% of the writing is from academic sources, it shows that the authors of those papers understand, not that the student understands. However, I also consider that the fact that the student knew which text to include should count for something.
Then I start thinking about plagiarism. If the student has simply quoted their way through a paper (with proper citations) then someone else could submit the same paper and it would not count as plagiarism because everything is cited.
Is there any generally accepted guideline on the percentage of writing in a student's written assignment which should be from the student and what percentage should be from other (hopefully academic) sources?
I realize that this might vary by field. My field is business management.