Do office hours really help raise student grades or are the students who use office hours simply more likely to study harder?
Actually, thinking about that makes my head hurt. But my purely ancedotal evidence suggests that it probably depends on the individual professor. I know this because I've had a lot of professors in my six years as an undergrad student.
My first ever office hours visit was to inquire about my grade. I didn't burst into tears, but my professor was kind enough to convince me that dropping out of school to become a long-haul truck driver was not in my best interest. (Two years later, it was an organic farming commune.)
I had another professor that I would go visit weekly (or so) in her damp, dimly lit bat cave. I liked her and she seemed to like me. We'd make small talk before going over (insert science-y type stuff here). The best part was that she would direct my attention to what topics would be heavily covered on the next test. I easily aced a class that many of my peers struggled in because I took the time to go visit her.
The last class that I felt compelled to go to office hours was also a science class. And I was struggling. I came prepared with specific questions and reference materials (my notes and the textbook, specifically). The professor, in all his wisdom, simply told me that I needed to "study harder." Then he rattled on about his sleep apnea and his wife's cancer before offering to drive me home. I politely declined, but I'm pretty sure that I could have slept with him for an A in the class.
I'm not certain what this all really means. Life's a crapshoot?