In an ideal world, I would completely agree with you. But anything close to 100% retention is extremely difficult to achieve, especially in math classes. I think some of the issues career colleges face stem from trying to cram a traditional semester or year's worth of material into an accelerated 10 week or less course format. Moreover, lax student admission policies also allow students that have not truly made a commitment to find the time to study hard and succeed in college to enroll in demanding classes. Once they start struggling because they have not put in the required effort or they miss a class or two, they lose hope and stop trying altogether. Being a stellar instructor and good person all around are definitely necessary for good retention rates, but they are surely not sufficient conditions. Students must also try to be responsible with their work, and the administration needs to effectively approach time constraints created by the course material (either break up a course into two or more consecutive courses or adjust prerequisites as needed).
