Do LOR writers need to be someone who's taught you a class? Background: (Undergrad applying For PhD in the US)
I need to submit 3 LOR's. I have one in mind from my personal university and 2 from other universities (with whom I have done extensive research with).
The one prof I plan to ask for an LOR from my personal university has not taught me in any class but I have done good amount of research with them (6-8 months). (This person has a professor grade with a doctorate and an extensive research portfolio and leads their own lab.)
I have another prof who has taught me several classes and I have done some research with them but have recently come in bad terms and I fear they might give me negative reviews. So I am quite skeptical of asking them now. (This person has a assistant-professor grade and no doctorate.)
Another reason why I ask this is because I am not a department topper and my courses at my university are quite mediocre, no stress upon lab components and no major project for any course. I even have mediocre attendance.
Question:
Is it okay if all 3 of my Letter writers did not teach me any class during my university tenure? Will it hamper my chances in any way?
Whether they taught you a class or not is irrelevant. What you need is people who can confidently and honestly predict your future success. This implies that having worked with someone in a research environment is probably more valuable than having them as an instructor.
In fact, given that many places now have very large classes and student interacting mostly with TAs, instructors may not be nearly as valuable as they once were.
So, no, it won't hamper you provided that your letter writers can make that prediction honestly and enthusiastically.