What do profs actually think when writing a letter of recommendation for an average student for grad school Grad school application starts now along with all the anxieties associated with it. 

One of the question I ask myself and repeatedly get asked by my peers is that what would the profs think when the transcript and resume reveals that they are just an average student (i.e. 3.3 GPA, at minimum of grad school acceptance requirement).

Of course, the top factor here is that we are being evaluated by people who are exceptionally talented and likely the top students back in their days. And plus we may have built an amicable relationship over a long period, no one wants to appear like a useless person. Lastly, there may exist a significant time period between when an application is sent out to when the letter is received, during this time I find a lot of students will question whether the profs are still open writing the letter for them.

What if a professor doesn't like what he sees in the transcript, or feel that the resume does not reflect any exceptional talent, what would a prof usually do in this case?
If you want to go to graduate school and think you will be successful, you should apply. Let the admissions committee decide your package.

I've written plenty of recommendation letters for more "average" students and I suspect most other faculty have too.

The only time I turn down a recommendation letter is if the student really did poorly (e.g., sub-3.0 GPA) in my classes. Then I gently suggest students find another letter-writer. This has only happened once.

Plenty of average students go to grad school and most of them get Ph.D.s. The degree is not necessarily an indication of exceptional brilliance. There are brilliant Ph.D. recipients, and there are less stellar Ph.D. recipients. Instead, the Ph.D. indicates a number of factors, including the ability to do independent research, a great deal of learning and advancement beyond a master's or bachelor's degree, and a huge amount of perseverance.

So I will write a letter appropriate to the student. I will indicate the grade they received in my class, or the research work they did in my group (e.g., "top third" or "top half of the graduating majors").

In terms of writing the recommendation letter, I try to stress positive points, but I am also honest to the admissions committee.

On the other side, the admissions committee knows how to read recommendation letters. There are many graduate programs, and not all programs expect the truly top students. So they can translate your application package into an evaluation of how likely you are to succeed in their program.