hra87 said:
Will associate professors work? Are there any schools that require full professors?
Associate professors are professors in every sense of the word and their letters, if they write positive ones, stand just as much a chance of helping you as do ones from full professors. Once you move into the domain of professors of any kind, the quality and import of a letter depends
much more on how well the writer knows you and esteems you as a scholar, student, or researcher than does the status of the letter writer (with exceptions made for a small number of extraordinary individuals).
For the majority of US colleges and universities, the hierarchy goes like this (be aware the terminology can vary widely, however, especially once you get into other countries' systems):
Assistant Professors: Recent Ph.D.s or at least recently hired into the department. Letters from assistant profs are perfectly fine. They are, after all, professors and that in and of itself is no small feat. Asst. profs usually have about 7 years to accumulate enough publications and other academic honors and service to be tenured. Once they are tenured, they are typically promoted to... (Note: if you're trying to get a letter from an asst. prof putting their tenure package together, buckle up, because they are almost certainly working balls to the wall and totally stressed out.)
Associate Professors: These are well established scholars with significant publications and many are quite well known (depending on how quickly they're rising through the ranks).
Full Professors: Actually there's a less siginificant difference between full and associate professors than there is between assistant and associate. Promotions from Associate to Full Professor status can vary according to the personal history of the individual in question, the department they're in, etc.
There are also other faculty positions whose presence and status can vary dramatically.
Visiting professors (whether asst., assoc., or full) are just that: people who are at the school temporarily and have been awarded a status comensurate, in the school's opinion, with their status. If you're going to get a letter from one of them, do it while they're on campus.
Lecturers: These are typically Ph.D.s who are hired (and re-hired) for specific periods of time but only to teach (usually lecturerships are not eligible for tenure). The value of their letters, much like those of profs, actually, derives from the fact that they usually have seen many students and have a solid basis for judging whether you're better than average.
