From my experience I have found that most student attrition comes from issues outside the classroom and the College. These issues can run the gambit from birth to death, marriage to divorce, and everything in between.

Let's face it, right after the midterm, students and faculty alike sometimes hit a wall, and don't put as much effort into their class as the beginning of the term. The excitement is gone, and the final is far enough away that they can't see the 'end is near'. It's very frustrating to see adjunct faculty dismissing their classes so early. What happened? Don't they realize they are cheating the students? These faculty don't realize they are not doing the students any favors, on the contrary, they are putting the students and the institution in jeopardy.